Perovskite materials and methods of making and use thereof

ABSTRACT

Disclosed herein are perovskite materials and methods of making an use thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to U.S. ProvisionalApplication No. 62/984,943 filed Mar. 4, 2020, which is herebyincorporated herein by reference in its entirety.

BACKGROUND

Research into Sn(II)-containing semiconductors has garnered significantinterest owing to their potential technological importance, such aswithin the fields of solar energy conversion, ferroelectrics andtransparent conducting oxides (TCOs). In the field of ferroelectrics,Sn(II)-containing perovskites have been intensely investigated asPb-free, isoelectronic versions of PbTiO₃ and PbZr_(0.5)Ti_(0.5)O₃. Oneof the most widely used ceramics in the electronics industry is leadzirconate titanate, known as ferroelectric PZT, which shows a strongpiezoelectric effect. This material contains over 60% highly toxic leadby weight and can cause significant safety issues during its processingand use, as lead is volatile and easily released into the environment.The toxicity of PZT also hinders important in vivo uses, as lead canslowly dissolve into a subject's bloodstream. While the increasing useof PZT represents a dangerous and growing concern, it also continues tobe mass produced and utilized in a plethora of products because thereare currently no suitable replacements for it. Precious fewSn(II)-containing oxides have been synthesized as compared to othermetal oxide systems. A primary reason is that, as a reactant, SnO iseasily oxidized in air and disproportionates when heated under vacuum orin an inert atmosphere beginning at ˜300° C. The compositions andmethods discussed herein addresses these and other needs.

SUMMARY

In accordance with the purposes of the disclosed compositions andmethods as embodied and broadly described herein, the disclosed subjectmatter relates to perovskite materials and methods of making and methodsof use thereof.

Additional advantages of the disclosed compositions and methods will beset forth in part in the description which follows, and in part will beobvious from the description. The advantages of the disclosedcompositions and methods will be realized and attained by means of theelements and combinations particularly pointed out in the appendedclaims. It is to be understood that both the foregoing generaldescription and the following detailed description are exemplary andexplanatory only and are not restrictive of the disclosed systems andmethods, as claimed.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

BRIEF DESCRIPTION OF THE FIGURES

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

The accompanying figures, which are incorporated in and constitute apart of this specification, illustrate several aspects of thedisclosure, and together with the description, serve to explain theprinciples of the disclosure.

FIG. 1 : Plot of Rietveld refinement of neutron diffraction data at roomtemperature for (Ba_(0.6)Sn_(0.4))(Zr_(0.5) Ti_(0.5))O₃.

FIG. 2 : Plot of Rietveld refinement of neutron diffraction data at roomtemperature for (Ba_(0.4)Sn_(0.6))(Zr_(0.5) Ti_(0.5))O₃.

FIG. 3 : Plot of Rietveld refinement of neutron diffraction data at 20 Kfor (Ba_(0.6)Sn_(0.4))(Zr_(0.5)Ti_(0.5))O₃.

FIG. 4 : Plot of Rietveld refinement of neutron diffraction data 20 Kfor (Ba_(0.4)Sn_(0.6))(Zr_(0.5)Ti_(0.5))O₃.

FIG. 5 . Pair distribution function refinement forBa(Zr_(0.5)Ti_(0.5))O₃. The cubic perovskite model was used forrefinement.

FIG. 6 . Pair distribution function refinement for(Ba_(0.8)Sn_(0.2))(Zr_(0.5)Ti_(0.5))O₃. The cubic perovskite model wasused for refinement.

FIG. 7 . Pair distribution function refinement for(Ba_(0.8)Sn_(0.2))(Zr_(0.25)Ti_(0.75))O₃. The cubic perovskite model wasused for refinement.

FIG. 8 . Pair distribution function refinement for(Ba_(0.4)Sn_(0.6))(Zr_(0.5)Ti_(0.5))O₃. The cubic perovskite model wasused for refinement.

FIG. 9 : SEM image of Ba(Zr_(0.5)Ti_(0.5))O₃. Particle sizes ranged ˜0.5to 2.0 μm.

FIG. 10 : SEM image of Ba(Zr_(0.5)Ti_(0.5))O₃. Particle sizes ranged˜0.5 to 2.0 μm.

FIG. 11 : SEM image of (Ba_(0.8)Sn_(0.2))(Zr_(0.5)Ti_(0.5))O₃. Particlesizes ranged ˜0.5 to 2.0 μm.

FIG. 12 : SEM image of (Ba_(0.8)Sn_(0.2))(Zr_(0.5)Ti_(0.5))O₃. Particlesizes ranged ˜0.5 to 2.0 μm.

FIG. 13 : SEM image of (Ba_(0.6)Sn_(0.4))(Zr_(0.5)Ti_(0.5))O₃. Particlesizes ranged ˜0.5 to 2.0 μm.

FIG. 14 : SEM image of (Ba_(0.6)Sn_(0.4))(Zr_(0.5)Ti_(0.5))O₃. Particlesizes ranged ˜0.5 to 2.0 μm.

FIG. 15 : SEM image of (Ba_(0.4)Sn_(0.6))(Zr_(0.5)Ti_(0.5))O₃. Particlesizes ranged ˜0.5 to 2.0 μm.

FIG. 16 : SEM image of (Ba_(0.4)Sn_(0.6))(Zr_(0.5)Ti_(0.5))O₃. Particlesizes ranged ˜0.5 to 2.0 μm.

FIG. 17 : Calculated reaction energy landscape for perovskitedecomposition at 0 K in the composition space spanningBaTiO₃—BaZrO₃—SnTiO₃—SnZrO₃, as representing the mixed A/A′- andB/B′-site solid solution Ba_(1-x)Sn_(x)Zr_(1-y)Ti_(y)O₃. The orange tored colors denote increasing instability and the light blue to dark bluecolors indicate increasing stability.

FIG. 18 : Experimentally observed indirect bandgap size of(Ba_(1-x)Sn_(x))(Zr_(1-y)Ti_(y))O₃ as a function of the Ba/Sn A-site(x-axis) and Zr/Ti B-site (y-axis) compositions. The blue to yellow tored colors indicate the decreasing bandgap sizes.

FIG. 19 : Experimentally observed direct bandgap transition of(Ba_(1-x)Sn_(x))(Zr_(1-y)Ti_(y))O₃ as a function of the Ba/Sn A-site(x-axis) and Zr/Ti B-site (y-axis) compositions. The blue to yellow tored colors indicate the decreasing bandgap sizes.

FIG. 20 : Both the indirect bandgap (FIG. 18 ) and direct bandgap (FIG.19 ) transitions of (Ba_(1-x)Sn_(x))(Zr_(1-y)Ti_(y))O₃ are plottedtogether as a function of the Ba/Sn A-site (x-axis) and Zr/Ti B-site(y-axis) compositions. The blue to yellow to red colors indicate thedecreasing bandgap sizes.

FIG. 21 : Plot of photocatalytic rate of suspended particles of(Ba_(1-x)Sn_(x))(Zr_(1-y)Ti_(y))O₃, as a function of the Ba/Sn A-site(x-axis) and Zr/Ti B-site (y-axis) compositions, for molecular oxygenevolution (μmol O₂ h⁻¹ g⁻¹) under combined ultraviolet+visible light(λ>230 nm) irradiation. The blue to red coloring denotes higherphotocatalytic rates.

FIG. 22 : Plot of photocatalytic rate of suspended particles of(Ba_(1-x)Sn_(x))(Zr_(1-y)Ti_(y))O₃, as a function of the Ba/Sn A-site(x-axis) and Zr/Ti B-site (y-axis) compositions, for molecular oxygenevolution (μmol O₂ h⁻¹ g⁻¹) under only visible-light irradiation (λ>400nm). The blue to red coloring denotes higher photocatalytic rates.

FIG. 23 : Plots of photocatalytic rates of suspended particles of(Ba_(1-x)Sn_(x))(Zr_(1-y)Ti_(y))O₃, as a function of the Ba/Sn A-site(x-axis) and Zr/Ti B-site (y-axis) compositions, for molecular oxygenevolution (μmol O₂ h⁻¹ g⁻¹) under combined ultraviolet+visible light(λ>230 nm) (FIG. 21 ) and under only visible-light irradiation (λ>400nm) (FIG. 22 ) plotted together. The blue to red coloring denotes higherphotocatalytic rates.

FIG. 24 . Schematic illustration of a TiO₆/ZrO₆ solid solution, red andwhite squares respectively, wherein the TiO₆ octahedra are mixed at aconcentration above the percolation threshold. The energy diagram(lower) shows the polaron hopping with activation barriers (E_(a))between the ZrO₆ or TiO₆ octahedra.

FIG. 25 . Schematic illustration of a TiO₆/ZrO₆ solid solution, red andwhite squares respectively, wherein the TiO₆ octahedra are mixed at aconcentration below the percolation threshold. The energy diagram(lower) show the polaron hopping with activation barriers (E_(a))between the ZrO₆ or TiO₆ octahedra.

FIG. 26 . PXRD for Ba_(1-x)Sn_(x)TiO₃ series (▴-ilmenite-type SnTiO₃).BaTiO₃ has a tetragonal P4MM perovskite structure while, SnTiO₃crystallizes in an ilmenite-type structure (R3-).

FIG. 27 . PXRD of Ba_(1-x)Sn_(x)Zr_(0.25)Ti_(0.75)O₃ series(▴-ilmenite-type SnTiO₃).

FIG. 28 . PXRD for Ba_(1-x)Sn_(x)Zr_(0.5)Ti_(0.5)O₃ series (•—ZrO₂,*—SnO)

FIG. 29 . PXRD for Ba_(1-x)Sn_(x)Zr_(0.75)Ti_(0.25)O₃ series (•—ZrO₂,*—SnO).

FIG. 30 . PXRD for the Ba_(1-x)Sn_(x)ZrO₃ series (*—SnO).

FIG. 31 . PXRD of pre-washed Ba_(1-x)Sn_(x)Zr_(0.5)Ti_(0.5)O₃ (*—BaClF).PXRD shows expected formation of BaClF in increasing amounts withincreasing Sn(II) concentration.

FIG. 32 . Plot of Rietveld refinement results of X-ray diffraction datafor Ba(Zr_(0.5)Ti_(0.5))O₃.

FIG. 33 . Plot of Rietveld refinement results of X-ray diffraction datafor (Ba_(0.8)Sn_(0.2))(Zr_(0.5)Ti_(0.5))O₃.

FIG. 34 . Plot of Rietveld refinement results of X-ray diffraction datafor (Ba_(0.6)Sn_(0.4))(Zr_(0.5)Ti_(0.5))O₃.

FIG. 35 . Plot of Rietveld refinement results of X-ray diffraction datafor (Ba_(0.4)Sn_(0.6))(Zr_(0.5) Ti_(0.5))O₃.

FIG. 36 . Representative EDS spectra for BSZT samples.Ba_(0.6)Sn_(0.4)Zr_(0.5)Ti_(0.5)O₃— shows detection limit level amountof Cl, likely as a result of trace amounts of BaClF that were notcompletely washed.

FIG. 37 . Representative EDS spectra for BSZT samples.Ba_(0.6)Sn_(0.4)ZrO₃— no signals for any remaining BaClF. C in bothsamples is from the C-tape.

FIG. 38 . Overlay of pair distribution function data forBa(Zr_(0.5)Ti_(0.5))O₃, (Ba_(0.8)Sn_(0.2))(Zr_(0.5)Ti_(0.5))O₃,(Ba_(0.4)Sn_(0.6))(Zr_(0.5)Ti_(0.5))O₃, and(Ba_(0.8)Sn_(0.2))(Zr_(0.25)Ti_(0.75))O₃. The profiles for the Sn(II)substituted phases match with cubic Ba(Zr_(0.5)Ti_(0.5))O₃. The datashows shifting consistent with lattice constant trends.

FIG. 39 . Cubic BSZT model with interatomic distances.

FIG. 40 . X-ray powder diffractograms forBa_(0.7)Sn_(0.3)Zr_(0.5)Ti_(0.5)O₃ synthesized at 350° C. for 12 h and400° C. for 24 h (•—ZrO₂, *—SnO). Ba_(0.7)Sn_(0.3)Zr_(0.5)Ti_(0.5)O₃,which could be successfully synthesized with only a small ZrO₂ sideproduct, shows significant formation of SnO and ZrO₂ with increasedreaction temperature and time.

FIG. 41 . X-ray powder diffractograms of products afterBa_(0.7)Sn_(0.3)Zr_(0.25)Ti_(0.75)O₃,Ba_(0.7)Sn_(0.3)Zr_(0.5)Ti_(0.5)O₃, and Ba_(0.7)Sn_(0.3)ZrO₃ were heatedto 800° C. for 8 h under vacuum (•—ZrO₂, •—SnO₂, V-Sn). The BSZT phasesall showed decomposition to binary oxides (SnO₂ and Sn are SnOdisproportionation products) with a perovskite phase remaining.

FIG. 42 . UV-Vis diffuse reflectance data as a Tauc plots of(F(R)×hv)^(n) versus hv (eV) where n=½ for indirect transitions forBa_(1-x)Sn_(x)TiO₃. The indirect transition was significantly redshifted compared to the parent BZT phase upon substitution of Sn(II).

FIG. 43 . UV-Vis diffuse reflectance data as a Tauc plots of(F(R)×hv)^(n) versus hv (eV) where n=½ for indirect transitions forBa_(1-x)Sn_(x)Zr_(0.25)Ti_(0.75)O₃. The indirect transition wassignificantly red shifted compared to the parent BZT phase uponsubstitution of Sn(II).

FIG. 44 . UV-Vis diffuse reflectance data as a Tauc plots of(F(R)×hv)^(n) versus hv (eV) where n=½ for indirect transitions forBa_(1-x)Sn_(x)Zr_(0.5)Ti_(0.5)O₃. The indirect transition wassignificantly red shifted compared to the parent BZT phase uponsubstitution of Sn(II).

FIG. 45 . UV-Vis diffuse reflectance data as a Tauc plots of(F(R)×hv)^(n) versus hv (eV) where n=½ for indirect transitions forBa_(1-x)Sn_(x)Zr_(0.75)Ti_(0.25)O₃. The indirect transition wassignificantly red shifted compared to the parent BZT phase uponsubstitution of Sn(II).

FIG. 46 . UV-Vis diffuse reflectance data as a Tauc plots of(F(R)×hv)^(n) versus hv (eV) where n=½ for indirect transitions forBa_(1-x)Sn_(x)ZrO₃. The indirect transition was significantly redshifted compared to the parent BZT phase upon substitution of Sn(II).

FIG. 47 . UV-Vis diffuse reflectance data as a Tauc plots of(F(R)×hv)^(n) versus hv (eV) where n=2 for direct transitions forBa_(1-x)Sn_(x)TiO₃.

FIG. 48 . UV-Vis diffuse reflectance data as a Tauc plots of(F(R)×hv)^(n) versus hv (eV) where n=2 for direct transitions forBa_(1-x)Sn_(x)Zr_(0.25)Ti_(0.75)O₃.

FIG. 49 . UV-Vis diffuse reflectance data as a Tauc plots of(F(R)×hv)^(n) versus hv (eV) where n=2 for direct transitions forBa_(1-x)Sn_(x)Zr_(0.5)Ti_(0.5)O_(3.)

FIG. 50 . UV-Vis diffuse reflectance data as a Tauc plots of(F(R)×hv)^(n) versus hv (eV) where n=2 for direct transitions forBa_(1-x)Sn_(x)Zr_(0.75)Ti_(0.25)O₃.

FIG. 51 . UV-Vis diffuse reflectance data as a Tauc plots of(F(R)×hv)^(n) versus hv (eV) where n=2 for direct transitions forBa_(1-x)Sn_(x)ZrO₃.

FIG. 52 . Densities-of-States (DOS) plot for Ba(Zr_(0.5)Ti_(0.5))O₃. Thecontributions of the individual atomic orbitals are represented bycolored lines and the total DOS by the black line. In each, the Fermilevel is located at 0 eV.

FIG. 53 . Densities-of-States (DOS) plot for(Ba_(0.4)Sn_(0.6))(Zr_(0.5)Ti_(0.5))O₃. The contributions of theindividual atomic orbitals are represented by colored lines and thetotal DOS by the black line. In each, the Fermi level is located at 0eV.

FIG. 54 . Photocatalytic rates of (Ba_(1-x)Sn_(x))(Zr_(1-y)Ti_(y))O₃ asa function of the Ba/Sn A-site (x-axis) and Zr/Ti B-site (y-axis)compositions, for molecular oxygen evolution. The highest photocatalyticactivities are found with increasing metastability and Sn(II)substitution, as highlighted in the diagram upon crossing from the blueto the red shaded regions.

DETAILED DESCRIPTION

The compositions and methods described herein may be understood morereadily by reference to the following detailed description of specificaspects of the disclosed subject matter and the Examples includedtherein.

Before the present compositions and methods are disclosed and described,it is to be understood that the aspects described below are not limitedto specific synthetic methods or specific reagents, as such may, ofcourse, vary. It is also to be understood that the terminology usedherein is for the purpose of describing particular aspects only and isnot intended to be limiting.

Also, throughout this specification, various publications arereferenced. The disclosures of these publications in their entiretiesare hereby incorporated by reference into this application in order tomore fully describe the state of the art to which the disclosed matterpertains. The references disclosed are also individually andspecifically incorporated by reference herein for the material containedin them that is discussed in the sentence in which the reference isrelied upon.

In this specification and in the claims that follow, reference will bemade to a number of terms, which shall be defined to have the followingmeanings.

Throughout the description and claims of this specification the word“comprise” and other forms of the word, such as “comprising” and“comprises,” means including but not limited to, and is not intended toexclude, for example, other additives, components, integers, or steps.

As used in the description and the appended claims, the singular forms“a,” “an,” and “the” include plural referents unless the context clearlydictates otherwise. Thus, for example, reference to “a composition”includes mixtures of two or more such compositions, reference to “anagent” includes mixtures of two or more such agents, reference to “thecomponent” includes mixtures of two or more such components, and thelike.

“Optional” or “optionally” means that the subsequently described eventor circumstance can or cannot occur, and that the description includesinstances where the event or circumstance occurs and instances where itdoes not.

Ranges can be expressed herein as from “about” one particular value,and/or to “about” another particular value. By “about” is meant within5% of the value, e.g., within 4, 3, 2, or 1% of the value. When such arange is expressed, another aspect includes from the one particularvalue and/or to the other particular value. Similarly, when values areexpressed as approximations, by use of the antecedent “about,” it willbe understood that the particular value forms another aspect. It will befurther understood that the endpoints of each of the ranges aresignificant both in relation to the other endpoint, and independently ofthe other endpoint.

It is understood that throughout this specification the identifiers“first” and “second” are used solely to aid in distinguishing thevarious components and steps of the disclosed subject matter. Theidentifiers “first” and “second” are not intended to imply anyparticular order, amount, preference, or importance to the components orsteps modified by these terms.

Perovskite Materials

Disclosed herein are perovskite materials comprising:[A_(1-x)Sn_(x)][B_(1-y)B′_(y)]O₃

-   -   where:    -   A, if present, is selected from the group consisting of Li, Na,        K, Rb, Cs, Be, Mg, Ca, Sr, Ba, Sc, Y, La, Ag, Cd, Tl, Pb, Ce,        Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, or a        combination thereof;    -   B and B′, if present, are independently selected from the group        consisting of Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge,        Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, La, Hf, Ta,        W, Re, Os, Ir, Pt, Au, Bi, or a combination thereof;    -   x is from greater than 0 to 1; and    -   y is from 0 to 1;    -   with the proviso that A and B are different, A and B′ are        different, and B and B′ are different.

In some examples, x is greater than 0 (e.g., 0.01 or more, 0.02 or more,0.03 or more, 0.04 or more, 0.05 or more, 0.06 or more, 0.07 or more,0.08 or more, 0.09 or more, 0.1 or more, 0.15 or more, 0.2 or more, 0.25or more, 0.3 or more, 0.35 or more, 0.4 or more, 0.45 or more, 0.5 ormore, 0.55 or more, 0.6 or more, 0.65 or more, 0.7 or more, 0.75 ormore, 0.8 or more, 0.85 or more, or 0.9 or more). In some examples, x is1 or less (e.g., 0.95 or less, 0.9 or less, 0.85 or less, 0.8 or less,0.75 or less, 0.7 or less, 0.65 or less, 0.6 or less, 0.55 or less, 0.5or less, 0.45 or less, 0.4 or less, 0.35 or less, 0.3 or less, 0.25 orless, 0.2 or less, 0.15 or less, 0.1 or less, 0.09 or less, 0.08 orless, 0.07 or less, 0.06 or less, or 0.05 or less). The value of x canrange from any of the minimum values described above to any of themaximum values described above. For example, x can be from greater than0 to 1 (e.g., from greater than 0 to 0.5, from 0.5 to 1, from greaterthan 0 to 0.4, from 0.4 to 0.7, from 0.7 to 1, from 0.1 to 1, fromgreater than 0 to 0.9, from 0.1 to 0.9, from 0.1 to 0.5, from 0.1 to0.4, from 0.2 to 1, from 0.4 to 1, from 0.6 to 1, from 0.8 to 1, from0.9 to 1, from 0.1 to 0.6, or from 0.5 to 0.6). In some examples, x is1.

In some examples, y is 0 or more (e.g., 0.05 or more, 0.1 or more, 0.15or more, 0.2 or more, 0.25 or more, 0.3 or more, 0.35 or more, 0.4 ormore, 0.45 or more, 0.5 or more, 0.55 or more, 0.6 or more, 0.65 ormore, 0.7 or more, 0.75 or more, 0.8 or more, 0.85 or more, 0.9 or more,or 0.95 or more). In some examples, y is 1 or less (e.g., 0.95 or less,0.9 or less, 0.85 or less, 0.8 or less, 0.75 or less, 0.7 or less, 0.65or less, 0.6 or less, 0.55 or less, 0.5 or less, 0.45 or less, 0.4 orless, 0.35 or less, 0.3 or less, 0.25 or less, 0.2 or less, 0.15 orless, 0.1 or less, or 0.05 or less). The value of y can range from anyof the minimum values described above to any of the maximum valuesdescribed above. For example, y can be from 0 to 1 (e.g., from 0 to 0.5,from 0.5 to 1, from 0 to 0.2, from 0.2 to 0.4, from 0.4 to 0.6, from 0.6to 0.8, from 0.8 to 1, from 0 to 0.9, from 0.1 to 1, from 0.1 to 0.9, orfrom 0.25 to 0.75). In some examples, y is 0. In some examples, y is 1.

In some examples, the perovskite material comprises[Ba_(1-x)Sn_(x)][Zr_(1-y)Ti_(y)]O₃. For example, the perovskite materialcan comprise [Ba_(1-x)Sn_(x)][Zr_(1-y)Ti_(y)]O₃, where x is from 0.1 to1 and y is 0, 0.25, 0.5, 0.75, or 1. In some examples, the perovskitematerial comprises [Ba_(1-x)Sn_(x)][Zr_(0.25)Ti_(0.75)]O₃, where x isfrom 0.1 to 0.4. In some examples, the perovskite material comprises[Ba_(1-x)Sn_(x)][Zr_(0.5)Ti_(0.5)]O₃, where x is from 0.1 to 0.6 (e.g.,wherein x is from 0.5 to 0.6). In some examples, the perovskite materialcomprises [Ba_(1-x)Sn_(x)]ZrO₃, where x is from 0.1 to 0.6 (e.g.,wherein is from 0.5 to 0.6). The perovskite material can, for example,comprise Ba_(0.8)Sn_(0.2)Zr_(0.25)Ti_(0.75)O₃,Ba_(0.8)Sn_(0.2)Zr_(0.5)Ti_(0.5)O₃, Ba_(0.6)Sn_(0.4)Zr_(0.5)Ti_(0.5)O₃,Ba_(0.4)Sn_(0.6)Zr_(0.5)Ti_(0.5)O₃,Ba_(0.8)Sn_(0.2)Zr_(0.75)Ti_(0.25)O₃, Ba_(0.8)Sn_(0.2)ZrO₃,Ba_(0.6)Sn_(0.4)ZrO₃, Ba_(0.9)Sn_(0.1)TiO₃, or a combination thereof.

In some examples, the perovskite material comprises[Pb_(1-x)Sn_(x)][Zr_(1-y)Ti_(y)]O₃. For example, the perovskite materialcam comprise [Pb_(1-x)Sn_(x)][Zr_(1-y)Ti_(y)]O₃ where x is from greaterthan 0 to 1 (e.g., wherein x is from 0.1 to 1, or from 0.5 to 1) and yis 0, 0.25, 0.5, 0.75, or 1.

In some examples, the perovskite material substantially excludes lead,such that the perovskite material comprises a lead-free perovskitematerial. In some examples, the perovskite material is biocompatible.

The perovskite materials described herein can, for example, have a cubicperovskite structure.

The perovskite materials described herein can, in some example, comprisea particle (e.g., a perovskite particle), e.g. also described herein areparticles comprising the perovskite materials described herein. As usedherein, “a perovskite particle” and “the perovskite particle” are meantto include any number of perovskite particles. Thus, for example “theperovskite particle” includes one or more perovskite particles. In someexamples, the perovskite particle can comprise a plurality of perovskiteparticles.

The perovskite particle can comprise a particle of any shape. Theperovskite particle can have an irregular shape, a regular shape, anisotropic shape, an anisotropic shape, or a combination thereof. In someexamples, the perovskite particle can have an isotropic shape. In someexamples, the perovskite particle can have an anisotropic shape. In someexamples, the perovskite particle can have a shape that is substantiallyspherical, ellipsoidal, triangular, pyramidal, tetrahedral, cylindrical,rectangular, cuboidal, or cuboctahedral. In some examples, theperovskite particle can have a shape that is substantially rectangular,cuboidal, or cuboctahedral.

The perovskite particle can have an average particle size. “Averageparticle size” and “mean particle size” are used interchangeably herein,and generally refer to the statistical mean particle size of theparticles in a population of particles. For example, the averageparticle size for a plurality of particles with a substantiallyspherical shape can comprise the average diameter of the plurality ofparticles. For a particle with a substantially spherical shape, thediameter of a particle can refer, for example, to the hydrodynamicdiameter. As used herein, the hydrodynamic diameter of a particle canrefer to the largest linear distance between two points on the surfaceof the particle. For an anisotropic particle, the average particle sizecan refer to, for example, the average maximum dimension of the particle(e.g., the length of a rod shaped particle, the diagonal of a cube shapeparticle, the bisector of a triangular shaped particle, etc.) For ananisotropic particle, the average particle size can refer to, forexample, the hydrodynamic size of the particle. Mean particle size canbe measured using methods known in the art, such as evaluation byscanning electron microscopy, transmission electron microscopy, and/ordynamic light scattering.

The perovskite particle can, for example, have an average particle sizeof 10 nm or more (e.g., 15 nm or more, 20 nm or more, 25 nm or more, 30nm or more, 35 nm or more, 40 nm or more, 45 nm or more, 50 nm or more,60 nm or more, 70 nm or more, 80 nm or more, 90 nm or more, 100 nm ormore, 125 nm or more, 150 nm or more, 175 nm or more, 200 nm or more,225 nm or more, 250 nm or more, 300 nm or more, 350 nm or more, 400 nmor more, 450 nm or more, 500 nm or more, 600 nm or more, 700 nm or more,800 nm or more, 900 nm or more, 1 micrometer (micron, μm) or more, 2microns or more, 3 microns or more, 4 microns or more, 5 microns ormore, 10 microns or more, 15 microns or more, 20 microns or more, 25microns or more, 30 microns or more, 35 microns or more, 40 microns ormore, 45 microns or more, 50 microns or more, 60 microns or more, 70microns or more, 80 microns or more, 90 microns or more, 100 microns ormore, 125 microns or more, 150 microns or more, 175 microns or more, 200microns or more, 225 microns or more, 250 microns or more, 300 micronsor more, 350 microns or more, 400 microns or more, 450 microns or more,500 microns or more, 600 microns or more, 700 microns or more, 800microns or more, or 900 microns or more). In some examples, theperovskite particle can have an average particle size of 1 millimeter(mm) or less (e.g., 900 microns or less, 800 microns or less, 700microns or less, 600 microns or less, 500 microns or less, 450 micronsor less, 400 microns or less, 350 microns or less, 300 microns or less,250 microns or less, 225 microns or less, 200 microns or less, 175microns or less, 150 microns or less, 125 microns or less, 100 micronsor less, 90 microns or less, 80 microns or less, 70 microns or less, 60microns or less, 50 microns or less, 45 microns or less, 40 microns orless, 35 microns or less, 30 microns or less, 25 microns or less, 20microns or less, 15 microns or less, 10 microns or less, 5 microns orless, 4 microns or less, 3 microns or less, 2 microns or less, 1 micronor less, 900 nm or less, 800 nm or less, 700 nm or less, 600 nm or less,500 nm or less, 450 nm or less, 400 nm or less, 350 nm or less, 300 nmor less, 250 nm or less, 225 nm or less, 200 nm or less, 175 nm or less,150 nm or less, 125 nm or less, 100 nm or less, 90 nm or less, 80 nm orless, 70 nm or less, 60 nm or less, 50 nm or less, 45 nm or less, 40 nmor less, 35 nm or less, 30 nm or less, 25 nm or less, 20 nm or less, or15 nm or less).

The average particle size of the perovskite particle can range from anyof the minimum values described above to any of the maximum valuesdescribed above. For example, the perovskite particle can have anaverage particle size of from 10 nm to 1 mm (e.g., from 10 nm to 100 nm,from 100 nm to 1 micron, from 1 micron to 10 microns, from 10 microns to100 microns, from 100 microns to 1 mm, from 1 nm to 500 nm, from 500 nmto 1 micron, from 1 micron to 500 microns, from 500 microns to 1 mm,from 125 nm to 5 microns, from 125 nm to 500 nm, from 100 nm to 5microns, or from 500 nm to 2 microns). The average particle size of theperovskite particle can, for example, be measured using electronmicroscopy.

In some examples, the perovskite particle can comprise a plurality ofperovskite particles, and the plurality of perovskite particles can besubstantially monodisperse. “Monodisperse” and “homogeneous sizedistribution,” as used herein, and generally describe a population ofparticles where all of the particles have the same or nearly the sameparticle size. As used herein, a monodisperse distribution refers toparticle distributions in which 80% of the distribution (e.g., 85% ofthe distribution, 90% of the distribution, or 95% of the distribution)lies within 25% of the average particle size (e.g., within 20% of theaverage particle size, within 15% of the average particle size, within10% of the average particle size, or within 5% of the average particlesize).

In some examples, the perovskite particle has a bandgap that overlapswith at least a portion of the solar spectrum. The size, shape, and/orcomposition of the perovskite particle can be selected in view of avariety of factors. In some examples, the size, shape, and/orcomposition can be selected such that the perovskite particle has abandgap that overlaps with at least a portion of the solar spectrum. Insome examples, the size, shape, and/or composition of the perovskiteparticle can be selected in view of the intended use of the perovskitematerial.

In some examples, the perovskite particle can comprise a plurality ofperovskite particles and the plurality of perovskite particles cancomprise: a first population of particles comprising a first materialand having a first average particle size and a first particle shape; anda second population of particles comprising a second material and havinga second average particle size and a second particle shape; wherein thefirst average particle size and the second average particle size aredifferent, the first particle shape and the second particle shape aredifferent, the first material and the second material are different, ora combination thereof. In some examples, the plurality of perovskiteparticles can comprise a mixture of a plurality of populations ofparticles, wherein each population of particles within the mixture has adifferent size, shape, composition, or combination thereof.

The perovskite materials described herein can, in some examples, bemetastable. For example, the perovskite materials can have a reactionenergy of 0.25 eV atom⁻¹ or more with respect to decomposition to asimpler oxide and/or to an ilmenite structure (e.g., 0.3 eV atom⁻¹ ormore, 0.35 eV atom⁻¹ or more, 0.4 eV atom⁻¹ or more, or 0.45 eV atom⁻¹or more). In some examples, the perovskite material can have a reactionenergy of 0.5 eV atom⁻¹ or less with respect to decomposition to asimpler oxide and/or to an ilmenite structure (e.g., 0.45 eV atom-1 orless, 0.4 eV atom⁻¹ or less, 0.35 eV atom⁻¹ or less, or 0.3 eV atom⁻¹ orless). The reaction energy of the perovskite material with respect todecomposition to a simpler oxide and/or to an ilmenite structure canrange from any of the minimum values described above to any of themaximum values described above. For example, the perovskite materialscan have a reaction energy of from 0.25 eV atom⁻¹ to 0.5 eV atom⁻¹ withrespect to decomposition to a simpler oxide and/or to an ilmenitestructure (e.g., from 0.25 eV atom⁻¹ to 0.35 eV atom⁻¹, from 0.35 eVatom⁻¹ to 0.5 eV atom⁻¹, from 0.25 eV atom⁻¹ to 0.3 eV atom⁻¹, from 0.3eV atom⁻¹ to 0.35 eV atom⁻¹, from 0.35 eV atom⁻¹ to 0.4 eV atom⁻¹, from0.45 eV atom⁻¹ to 0.5 eV atom⁻¹, from 0.3 eV atom⁻¹ to 0.5 eV atom⁻¹,from 0.25 eV atom⁻¹ to 0.45 eV atom⁻¹, from 0.3 eV atom⁻¹ to 0.45 eVatom⁻¹, from 0.3 eV atom⁻¹ to 0.5 eV atom⁻¹, or from 0.4 eV atom⁻¹ to0.5 eV atom⁻¹).

In some examples, the perovskite material is ferroelectric. In someexamples, the perovskite material comprises a lead-free ferroelectricmaterial.

In some examples, the perovskite material comprises a semiconductor witha bandgap that overlaps with at least a portion of the solar spectrum.For example, the perovskite material can comprise a semiconductor with abandgap of 1.6 eV or more (e.g., 1.65 eV or more, 1.7 eV or more, 1.75eV or more, 1.8 eV or more, 1.85 eV or more, 1.9 eV or more, 1.95 eV ormore, 2 eV or more, 2.1 eV or more, 2.2 eV or more, 2.3 eV or more, 2.4eV or more, 2.5 eV or more, 2.6 eV or more, 2.7 eV or more, 2.8 eV ormore, 2.9 eV or more, 3 eV or more, 3.1 eV or more, 3.2 eV or more, 3.3eV or more, 3.4 eV or more, 3.5 eV or more, 3.6 eV or more, 3.7 eV ormore, or 3.8 eV or more). In some examples, the perovskite material cancomprise a semiconductor with a bandgap of 3.9 eV or less (e.g., 3.8 eVor less, 3.7 eV or less, 3.6 eV or less, 3.5 eV or less, 3.4 eV or less,3.3 eV or less, 3.2 eV or less, 3.1 eV or less, 3 eV or less, 2.9 eV orless, 2.8 eV or less, 2.7 eV or less, 2.6 eV or less, 2.5 eV or less,2.4 eV or less, 2.3 eV or less, 2.2 eV or less, 2.1 eV or less, 2 eV orless, 1.95 eV or less, 1.9 eV or less, 1.85 eV or less, 1.8 eV or less,1.75 eV or less, or 1.7 eV or less). The bandgap can range from any ofthe minimum values described above to any of the maximum valuesdescribed above. For example, the perovskite can comprise asemiconductor with a bandgap of from 1.6 eV to 3.9 eV (e.g., from 1.6 eVto 2.8 eV, from 2.8 eV to 3.9 eV, from 1.6 eV to 2 eV, from 2 eV to 2.4eV, from 2.4 eV to 2.8 eV, from 2.8 eV to 3.2 eV, from 3.2 eV to 3.6 eV,from 3.6 eV to 2.9 eV, from 1.6 eV to 3.8 eV, from 1.7 eV to 3.9 eV,from 1. eV 7 to 3.8 eV, or from 1.95 eV to 3 eV).

The perovskite material can, for example, comprise a photocatalyst. Insome examples, the perovskite material comprises a photocatalyst thatexhibits a photocatalytic rate of 100 μmol O₂ h⁻¹ g⁻¹ or more (e.g., 125μmol O₂ h⁻¹ g⁻¹ or more, 150 μmol O₂ h⁻¹ g⁻¹ or more, 175 μmol O₂ h⁻¹g⁻¹ or more, 200 μmol O₂ h⁻¹ g⁻¹ or more, 225 μmol O₂ h⁻¹ g⁻¹ or more,250 μmol O₂ h⁻¹ g⁻¹ or more, 275 μmol O₂ h⁻¹ g⁻¹ or more, 300 μmol O₂h⁻¹ g⁻¹ or more, 325 μmol O₂ h⁻¹ g⁻¹ or more, 350 μmol O₂ h⁻¹ g⁻¹ ormore, 375 μmol O₂ h⁻¹ g⁻¹ or more, 400 μmol O₂ h⁻¹ g⁻¹ or more, 425 μmolO₂ h⁻¹ g⁻¹ or more, 450 μmol O₂ h⁻¹ g⁻¹ or more, 475 μmol O₂ h⁻¹ g⁻¹ ormore, 500 μmol O₂ h⁻¹ g⁻¹ or more, 550 μmol O₂ h⁻¹ g⁻¹ or more, 600 μmolO₂ h⁻¹ g⁻¹ or more, 650 μmol O₂ h⁻¹ g⁻¹ or more, 700 μmol O₂ h⁻¹ g⁻¹ ormore, 750 μmol O₂ h⁻¹ g⁻¹ or more, 800 μmol O₂ h⁻¹ g⁻¹ or more, 850 μmolO₂ h⁻¹ g⁻¹ or more, 900 μmol O₂ h⁻¹ g⁻¹ or more, 950 μmol O₂ h⁻¹ g⁻¹ ormore, 1000 μmol O₂ h⁻¹ g⁻¹ or more, 1100 μmol O₂ h⁻¹ g⁻¹ or more, 1200μmol O₂ h⁻¹ g⁻¹ or more, 1300 μmol O₂ h⁻¹ g⁻¹ or more, 1400 μmol O₂ h⁻¹g⁻¹ or more, 1500 μmol O₂ h⁻¹ g⁻¹ or more, 2000 μmol O₂ h⁻¹ g⁻¹ or more,2500 μmol O₂ h⁻¹ g⁻¹ or more, 3000 μmol O₂ h⁻¹ g⁻¹ or more, 3500 μmol O₂h⁻¹ g⁻¹ or more, 4000 μmol O₂ h⁻¹ g⁻¹ or more, or 4500 μmol O₂ h⁻¹ g⁻¹or more). In some examples, the perovskite material comprises aphotocatalyst that exhibits a photocatalytic rate of 5000 μmol 02 h⁻¹g⁻¹ or less (e.g., 4500 μmol O₂ h⁻¹ g⁻¹ or less, 4000 μmol O₂ h⁻¹ g⁻¹ orless, 3500 μmol O₂ h⁻¹ g⁻¹ or less, 3000 μmol O₂ h⁻¹ g⁻¹ or less, 2500μmol O₂ h⁻¹ g⁻¹ or less, 2000 μmol O₂ h⁻¹ g⁻¹ or less, 1500 μmol O₂ h⁻¹g⁻¹ or less, 1400 μmol O₂ h⁻¹ g⁻¹ or less, 1300 μmol O₂ h⁻¹ g⁻¹ or less,1200 μmol O₂ h⁻¹ g⁻¹ or less, 1100 μmol O₂ h⁻¹ g⁻¹ or less, 1000 μmol O₂h⁻¹ g⁻¹ or less, 950 μmol O₂ h⁻¹ g⁻¹ or less, 900 μmol O₂ h⁻¹ g⁻¹ orless, 850 μmol O₂ h⁻¹ g⁻¹ or less, 800 μmol O₂ h⁻¹ g⁻¹ or less, 750 μmolO₂ h⁻¹ g⁻¹ or less, 700 μmol O₂ h⁻¹ g⁻¹ or less, 650 μmol O₂ h⁻¹ g⁻¹ orless, 600 μmol O₂ h⁻¹ g⁻¹ or less, 550 μmol O₂ h⁻¹ g⁻¹ or less, 500 μmolO₂ h⁻¹ g⁻¹ or less, 475 μmol O₂ h⁻¹ g⁻¹ or less, 450 μmol O₂ h⁻¹ g⁻¹ orless, 425 μmol O₂ h⁻¹ g⁻¹ or less, 400 μmol O₂ h⁻¹ g⁻¹ or less, 375 μmolO₂ h⁻¹ g⁻¹ or less, 350 μmol O₂ h⁻¹ g⁻¹ or less, 325 μmol O₂ h⁻¹ g⁻¹ orless, 300 μmol O₂ h⁻¹ g⁻¹ or less, 275 μmol O₂ h⁻¹ g⁻¹ or less, 250 μmolO₂ h⁻¹ g⁻¹ or less, 225 μmol O₂ h⁻¹ g⁻¹ or less, 200 μmol O₂ h⁻¹ g⁻¹ orless, 175 μmol O₂ h⁻¹ g⁻¹ or less, or 150 μmol O₂ h⁻¹ g⁻¹ or less). Thephotocatalytic rate exhibited by the perovskite material can range fromany of the minimum values described above to any of the maximum valuesdescribed above. For example, the perovskite material comprises aphotocatalyst that exhibits a photocatalytic rate from 100 μmol O₂ h⁻¹g⁻¹ to 5000 μmol O₂ h⁻¹ g⁻¹ (e.g., from 100 μmol O₂ h⁻¹ g⁻¹ to 500 μmolO₂ h⁻¹ g⁻¹, from 500 μmol O₂ h⁻¹ g⁻¹ to 1000 μmol O₂ h⁻¹ g⁻¹, from 1000μmol O₂ h⁻¹ g⁻¹ to 5000 μmol O₂ h⁻¹ g⁻¹, from 100 μmol O₂ h⁻¹ g⁻¹ to1000 μmol O₂ h⁻¹ g⁻¹, or from 500 μmol O₂ h⁻¹ g⁻¹ to 5000 μmol O₂ h⁻¹g⁻¹).

The perovskite material can comprise a photocatalyst that exhibits aphotocatalytic rate from 100 μmol O₂ h⁻¹ g⁻¹ to 5000 μmol O₂ h⁻¹ g⁻¹under electromagnetic irradiation at one or more wavelengths of 230 nmor more (e.g., 240 nm or more, 250 nm or more, 260 nm or more, 270 nm ormore, 280 nm or more, 290 nm or more, 300 nm or more, 325 nm or more,350 nm or more, 375 nm or more, 400 nm or more, 425 nm or more, 450 nmor more, 475 nm or more, 500 nm or more, 525 nm or more, 550 nm or more,575 nm or more, 600 nm or more, 625 nm or more, 650 nm or more, 675 nmor more, 700 nm or more, 750 nm or more, 800 nm or more, 850 nm or more,900 nm or more, or 950 nm or more). In some examples, the perovskitematerial can comprise a photocatalyst that exhibits a photocatalyticrate from 100 μmol O₂ h⁻¹ g⁻¹ to 5000 μmol O₂ h⁻¹ g⁻¹ underelectromagnetic irradiation at one or more wavelengths of 1023 nm orless (e.g., 1000 nm or less, 950 nm or less, 900 nm or less, 850 nm orless, 800 nm or less, 750 nm or less, 700 nm or less, 675 nm or less,650 nm or less, 625 nm or less, 600 nm or less, 575 nm or less, 550 nmor less, 525 nm or less, 500 nm or less, 475 nm or less, 450 nm or less,425 nm or less, 400 nm or less, 375 nm or less, 350 nm or less, 325 nmor less, 300 nm or less, 290 nm or less, 280 nm or less, 270 nm or less,260 nm or less, or 250 nm or less). The perovskite material can comprisea photocatalyst that exhibits a photocatalytic rate from 100 μmol O₂ h⁻¹g⁻¹ to 5000 μmol O₂ h⁻¹ g⁻¹ under electromagnetic irradiation at one ormore wavelengths that range from any of the minimum values describedabove to any of the maximum values described above. For example, theperovskite material can comprise a photocatalyst that exhibits aphotocatalytic rate from 100 μmol O₂ h⁻¹ g⁻¹ to 5000 μmol O₂ h⁻¹ g⁻¹under electromagnetic irradiation at one or more wavelengths from 230 nmto 1023 nm (e.g., from 230 nm to 700 nm, from 700 nm to 1023 nm, from230 nm to 575 nm, from 400 nm to 575 nm, from 400 nm to 1023 nm, or from575 nm to 1023 nm).

In some examples, the perovskite material comprises a photocatalyst thatexhibits an apparent quantum yield of 0.3% or more (e.g., 0.35% or more,0.4% or more, 0.45% or more, 0.5% or more, 0.6% or more, 0.7% or more,0.8% or more, 0.9% or more, 1% or more, 1.25% or more, 1.5% or more,1.75% or more, 2% or more, 2.25% or more, 2.5% or more, 3% or more, 3.5%or more, 4% or more, 4.5% or more, 5% or more, 6% or more, 7% or more,8% or more, 9% or more, 10% or more, 15% or more, 20% or more, 25% ormore, 30% or more, 35% or more, or 40% or more). In some examples, theperovskite material can comprise a photocatalyst that exhibits anapparent quantum yield of 50% or less (e.g., 45% or less, 40% or less,35% or less, 30% or less, 25% or less, 20% or less, 15% or less, 10% orless, 9% or less, 8% or less, 7% or less, 6% or less, 5% or less, 4.5%or less, 4% or less, 3.5% or less, 3% or less, 2.5% or less, 2.25% orless, 2% or less, 1.75% or less, 1.5% or less, 1.25% or less, 1% orless, 0.9% or less, 0.8% or less, 0.7% or less, 0.6% or less, 0.5% orless, 0.45% or less, or 0.4% or less). The apparent quantum yieldexhibited by the perovskite material can range from any of the minimumvalues described above to any of the maximum values described above. Forexample, the perovskite material can comprise a photocatalyst thatexhibits an apparent quantum yield of from 0.3% to 50% (e.g., from 0.3%to 1%, from 1% to 10%, from 10% to 50%, from 0.3% to 40%, from 0.5% to50%, or from 1% to 50%).

Also described herein are films comprising the perovskite materialsdescribed herein. The films can, for example, have a thickness of 100 nmor more (e.g., 125 nm or more, 150 nm or more, 175 nm or more, 200 nm ormore, 225 nm or more, 250 nm or more, 300 nm or more, 350 nm or more,400 nm or more, 450 nm or more, 500 nm or more, 600 nm or more, 700 nmor more, 800 nm or more, 900 nm or more, 1 micrometer (micron, μm) ormore, 1.25 microns or more, 1.5 microns or more, 1.75 microns or more, 2microns or more, 2.25 microns or more, 2.5 microns or more, 2.75 micronsor more, 3 microns or more, 3.25 microns or more, 3.5 microns or more,3.75 microns or more, 4 microns or more, 4.25 microns or more, or 4.5microns or more). In some examples, the films can have a thickness of 5microns or less (e.g., 4.75 microns or less, 4.5 microns or less, 4.25microns or less, 4 microns or less, 3.75 microns or less, 3.5 microns orless, 3.25 microns or less, 3 microns or less, 2.75 microns or less, 2.5microns or less, 2.25 microns or less, 2 microns or less, 1.75 micronsor less, 1.5 microns or less, 1.25 microns or less, 1 micron or less,900 nm or less, 800 nm or less, 700 nm or less, 600 nm or less, 500 nmor less, 450 nm or less, 400 nm or less, 350 nm or less, 300 nm or less,250 nm or less, 225 nm or less, 200 nm or less, 175 nm or less, or 150nm or less). The thickness of the films can range from any of theminimum values described above to any of the maximum values describedabove. For example, the films can have a thickness of from 100nanometers to 5 micrometers (e.g., from 100 nm to 500 nm, from 500 nm to1 micron, from 1 micron to 5 microns, from 100 nm to 4 microns, from 200nm to 5 microns, or from 200 nm to 4 microns).

Methods of Making

Also disclosed herein are methods of making perovskite materials, suchas metastable perovskite materials. Also disclosed herein are methods ofmaking the perovskite materials disclosed herein. The methods can, forexample, comprise a peritectic flux reaction between a preliminaryperovskite material and a Sn(II)-halide salt. The term “preliminaryperovskite material” is used herein to refer to a perovskite materialbefore it has undergone a peritectic flux reaction with a Sn(II)-halidesalt as described herein. It is not meant to imply that the preliminaryperovskite material is not yet a perovskite material. For example, thepreliminary perovskite material can comprise a perovskite having aformula A[B_(1-y)B′_(y)]O₃. In some examples, the preliminary perovskitecomprises lead zirconate titanate (PZT).

In some examples, the method comprises contacting a preliminaryperovskite comprising A[B_(1-y)B′_(y)]O₃ with a Sn(II)-halide saltcomprising SnCl₂ and/or SnF₂. In some examples, the preliminaryperovskite comprises lead zirconate titanate (PZT). For example, themethods described herein can comprise converting a lead-containingperovskite to a lead-free perovskite by extracting the lead from thelead-containing perovskite.

The method can, for example, be performed at a temperature of 20° C. ormore (e.g., 25° C. or more, 30° C. or more, 35° C. or more, 40° C. ormore, 45° C. or more, 50° C. or more, 60° C. or more, 70° C. or more,80° C. or more, 90° C. or more, 100° C. or more, 125° C. or more, 150°C. or more, 175° C. or more, 200° C. or more, 225° C. or more, 250° C.or more, 275° C. or more, 300° C. or more, 325° C. or more, 350° C. ormore, 375° C. or more, 400° C. or more, 425° C. or more, or 450° C. ormore). In some examples, the method can be performed at a temperature of500° C. or less (e.g., 475° C. or less, 450° C. or less, 425° C. orless, 400° C. or less, 375° C. or less, 350° C. or less, 325° C. orless, 300° C. or less, 275° C. or less, 250° C. or less, 225° C. orless, 200° C. or less, 175° C. or less, 150° C. or less, 125° C. orless, 100° C. or less, 90° C. or less, 80° C. or less, 70° C. or less,60° C. or less, 50° C. or less, 45° C. or less, 40° C. or less, 35° C.or less, or 30° C. or less). The temperature at which the method isperformed can range from any of the minimum values described above toany of the maximum values described above. For example, the method canbe performed at a temperature of from 20° C. to 500° C. (e.g., from 20°C. to 250° C., from 250° C. to 500° C., from 20° C. to 100° C., from100° C. to 200° C., from 200° C. to 300° C., from 300° C. to 400° C.,from 400° C. to 500° C., from 20° C. to 400° C., from 20° C. to 350° C.,from 50° C. to 350° C., or from 50° C. to 250° C.).

In some examples, the preliminary perovskite can be contacted with theSn(II)-halide salt for an amount of time of 5 minutes or more (e.g., 10minutes or more, 15 minutes or more, 20 minutes or more, 25 minutes ormore, 30 minutes or more, 35 minutes or more, 40 minutes or more, 45minutes or more, 50 minutes or more, 55 minutes or more, 1 hour or more,1.5 hours or more, 2 hours or more, 2.5 hours or more, 3 hours or more,3.5 hours or more, 4 hours or more, 4.5 hours or more, 5 hours or more,5.5 hours or more, 6 hours or more, 7 hours or more, 8 hours or more, 9hours or more, 10 hours or more, 11 hours or more, 12 hours or more, 14hours or more, 16 hours or more, 18 hours or more, 20 hours or more, or22 hours or more). In some examples, the preliminary perovskite can becontacted with the Sn(II)-halide salt for an amount of time of 24 hoursor less (e.g., 22 hours or less, 20 hours or less, 18 hours or less, 16hours or less, 14 hours or less, 12 hours or less, 11 hours or less, 10hours or less, 9 hours or less, 8 hours or less, 7 hours or less, 6hours or less, 5.5 hours or less, 5 hours or less, 4.5 hours or less, 4hours or less, 3.5 hours or less, 3 hours or less, 2.5 hours or less, 2hours or less, 1.5 hours or less, 1 hours or less, 55 minutes or less,50 minutes or less, 45 minutes or less, 40 minutes or less, 35 minutesor less, 30 minutes or less, 25 minutes or less, 20 minutes or less, 15minutes or less, or 10 minutes or less). The amount of time that thepreliminary perovskite can be contacted with the Sn(II)-halide salt canrange from any of the minimum values described above to any of themaximum values described above. For example, preliminary perovskite canbe contacted with the Sn(II)-halide salt for an amount of time of from 5minutes to 24 hours (e.g., from 5 minutes to 1 hour, from 1 hour to 12hours, from 12 hours to 24 hours, from 5 minutes to 12 hours, from 10minutes to 30 minutes, or from 10 hours to 14 hours).

The method can, for example, be performed under vacuum and/or an inertatmosphere (e.g., Ar, N₂, etc.).

In some examples, the preliminary perovskite material is contacted withthe Sn(II)-halide salt for a first amount of time (e.g., from 10 minutesto 30 minutes) at a first temperature (from 20° C. to 50° C.) under aninert atmosphere (e.g., argon), and subsequently for a second amount oftime (e.g., from 10 hours to 14 hours) at a second temperature (e.g.,from 300° C. to 400° C.) under vacuum. In some examples, after thesecond amount of time, the methods can further comprise cooling theperovskite material. In some examples, the methods can further comprisesubsequently washing and then drying the perovskite material.

Devices and Methods of Use

Also disclosed herein are methods of use of the perovskite materialsdescribed herein.

For example, the methods can comprise using the perovskite material as aferroelectric, transparent conducting oxide, dielectric, or acombination thereof. In some examples, the methods can comprise usingthe perovskite material as a photocatalyst.

Also disclosed herein are methods of using the perovskite materialsdescribed herein as a photocatalyst for photocatalytic fuel generation.The methods can comprise, for example, contacting the photocatalyst witha fuel precursor to form a mixture and illuminating the mixture withlight that overlaps with at least a portion of the bandgap of theperovskite material, thereby converting the fuel precursor to a fuel.

The light can, for example, be provided by a light source. The lightsource can be any type of light source. Examples of suitable lightsources include natural light sources (e.g., sunlight) and artificiallight sources (e.g., incandescent light bulbs, light emitting diodes,gas discharge lamps, arc lamps, lasers, etc.). In some examples, thelight comprises sunlight.

In some examples, the fuel precursor comprises water. The methods can,for example, comprise using the perovskite material as a photocatalystfor solar water splitting.

In some examples, the fuel comprises hydrogen. The methods can comprise,for example, using the perovskite material as a photocatalyst forphotocatalytic hydrogen generation.

In some examples, the perovskite material comprises a photocatalyst thatexhibits a photocatalytic rate of from 100 μmol O₂ h⁻¹ g⁻¹ to 5000 μmolO₂ h⁻¹ g⁻¹ under electromagnetic irradiation at one or more wavelengthsfrom 230 nm to 1023 nm. In some examples, the perovskite materialcomprises a photocatalyst that exhibits an apparent quantum yield offrom 0.3% to 50%.

In some examples, the perovskite materials can be used in variousdevices and articles of manufacture, such as sensors (e.g.,biocompatible sensors), energy conversion devices (e.g., solar cells,fuel cells, photovoltaic cells, piezoelectric devices), charge storagedevices (e.g., batteries, capacitors), electronic devices, and the like.Such articles of manufacture of devices can be fabricated by methodsknown in the art.

In some examples, the perovskite materials can be used as/in apiezoelectric device, wherein the piezoelectric device comprises anactuator, a motor, a sensor (e.g., a biocompatible sensor), atransducer, a high voltage source, a power source (e.g., apiezo-electric-powered pacemaker). In some examples, the methods cancomprise using the piezoelectric device in ultrasound, an electriclighter, a microphone, a fuse, a guitar pickup, an inkjet printer, aloudspeaker, laser electronics, an automotive application, or acombination thereof. In some examples, the method can comprise using thepiezoelectric device in an automotive application in a motor, anactuator, a power source, or a combination thereof.

Also disclosed herein are devices and articles of manufacture comprisingthe perovskite materials described herein. Such articles of manufactureof devices can be fabricated by methods known in the art. In someexamples, the device comprises a ferroelectric device, a transparentconducting oxide device, a dielectric device, or a combination thereof.In some examples, the device comprises a sensor (e.g., a biocompatiblesensor), an energy conversion device (e.g., a solar cell, a fuel cell, aphotovoltaic cell, a piezoelectric device), a charge storage device(e.g., a battery, a capacitor), an electronic device, or a combinationthereof.

In some examples, the device comprises a piezoelectric device, e.g.,also disclosed herein are piezoelectric devices comprising theperovskite materials described herein. The piezoelectric device can, forexample, comprise an actuator, a motor, a sensor (e.g., a biocompatiblesensor), a transducer, a high voltage source, a power source (e.g., apiezoelectric-powered pacemaker). In some examples, the piezoelectricdevice comprises a power source in a pacemaker. Also described hereinare methods of use of the piezoelectric devices described herein. Forexample, the methods can comprise using the piezoelectric device as anactuator, a motor, a sensor (e.g., a biocompatible sensor), atransducer, a high voltage source, a power source (e.g., in apiezo-electric-powered pacemaker). In some examples, the methodcomprises using the piezoelectric device in ultrasound, an electriclighter, a microphone, a fuse, a guitar pickup, an inkjet printer, aloudspeaker, laser electronics, an automotive application, or acombination thereof. In some examples, the method comprises using thepiezoelectric device in an automotive application in a motor, anactuator, a power source, or a combination thereof.

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention.Accordingly, other embodiments are within the scope of the followingclaims.

The examples below are intended to further illustrate certain aspects ofthe systems and methods described herein, and are not intended to limitthe scope of the claims.

EXAMPLES

The following examples are set forth below to illustrate the methods andresults according to the disclosed subject matter. These examples arenot intended to be inclusive of all aspects of the subject matterdisclosed herein, but rather to illustrate representative methods andresults. These examples are not intended to exclude equivalents andvariations of the present invention which are apparent to one skilled inthe art.

Efforts have been made to ensure accuracy with respect to numbers (e.g.,amounts, temperature, etc.) but some errors and deviations should beaccounted for. Unless indicated otherwise, parts are parts by weight,temperature is in ° C. or is at ambient temperature, and pressure is ator near atmospheric. There are numerous variations and combinations ofmeasurement conditions, e.g., component concentrations, temperatures,pressures and other measurement ranges and conditions that can be usedto optimize the described process.

Example 1—Metastable Semiconducting Perovskite Oxides forVisible-Light-Driven Water Oxidation

Described herein is a synthetic route to thermodynamically unstable,i.e., metastable, Sn(II)-perovskite oxides that have been highly soughtafter as lead-free dielectrics and small bandgap semiconductors. Anexchange of Sn(II) is found using a low melting SnCl₂/SnF₂ peritecticflux, yielding mixed A-site (Ba_(1-x)Sn_(x))ZrO₃ and mixed A- and B-site(Ba_(1-x)Sn_(x))(Zr_(1-y)Ti_(y))O₃ (BSZT) solid solutions that exhibithigh metastability, with up to 60% Sn(II) cations and a calculatedreaction energy for decomposition of up to −0.3 eV atom⁻¹. Kineticstabilization of the higher Sn(II) concentrations can be achieved by thehigh cohesive energy of the perovskite compositions containing Zr(IV)and mixed Zr(IV)/Ti(IV) cations. Red-shifted band gaps are found withincreasing Sn(II) substitution, enabling the optical absorption edge tobe broadly tuned from ˜3.90 eV to ˜1.95 eV. Percolation pathways arecalculated to occur for BSZT compositions with >10% Sn(II) and >25%Ti(IV) cations. High photocatalytic rates are found for molecular oxygenproduction for compositions which exceed the percolation thresholds,wherein extended diffusion pathways should ‘open up’ across thestructure and the charge carriers become delocalized rather thantrapped. These results indicate that it can be important tosynthetically access metastable semiconductors for the discovery ofadvanced optical and photocatalytic properties.

Introduction. Research into Sn(II)-containing semiconductors hasgarnered significant interest owing to their potential technologicalimportance, such as within the fields of solar energy conversion,ferroelectrics and transparent conducting oxides (TCOs) (Noureldine etal. Catal. Sci. Technol. 2016, 6 (21), 7656-7670; Ha et al. J. Mater.Chem. C 2017, 5 (23), 5772-5779; Matar et al. Chem. Phys. 2009, 355 (1),43-49). Intriguing optical properties of Sn(II)-containing oxidesinclude their small semiconducting band gaps, e.g., −1.6 to 2.0 eV, as aresult of the high energy valence band formed by the filled O 2p/Sn 5 sstates. These semiconductors can also exhibit a large valence banddispersion originating from the extended —O—Sn—O—Sn-connectivity andcoordination geometries. Consequently, relatively low effective massesand high carrier mobilities are achievable, as highly desired insemiconductor applications such as in photovoltaics, photocatalysis andTCOs. In the field of ferroelectrics, the perovskite-type SnTiO₃,SnZr_(0.5)Ti_(0.5)O₃ and related phases have been intensely investigatedas Pb-free, isoelectronic versions of PbTiO₃ and PbZr_(0.5)Ti_(0.5)O₃(Ribeiro et al. J. Alloys. Compds. 2017, 714, 553-559; Gardner et al.Reports Prog. Phys. 2019, 82, 092501; Parker et al. Phys. Rev.B—Condens. Matter Mater. Phys. 2011, 84 (24), 1-7; Pitike et al. Phys.Rev. B—Condens. Matter Mater. Phys. 2015, 91 (3), 1-8; Campo et al.Heliyon 2016, 2 (5), e00112). The latter perovskite is one of the mostwidely used ceramics in the electronics industry because of its strongpiezoelectric effect. Prior computational studies on the structure ofSnTiO₃ have posited the occurrence of a very high ferroelectricpolarization (˜1.1 C·m²) resulting from a stronger tetragonal distortionas compared to PbTiO₃ (Parker et al. Phys. Rev. B—Condens. Matter Mater.Phys. 2011, 84 (24), 1-7; Pitike et al. Phys. Rev. B—Condens. MatterMater. Phys. 2015, 91 (3), 1-8). However, the bulk syntheses of SnTiO₃and SnZr_(0.5)Ti_(0.5)O₃ have so far eluded attempts by manylaboratories worldwide (Gardner et al. Reports Prog. Phys. 2019, 82,092501).

Precious few Sn(II)-containing oxides have been synthesized as comparedto other metal oxide systems. A primary reason is that, as a reactant,SnO is easily oxidized in air and disproportionates when heated undervacuum or in an inert atmosphere beginning at ˜300° C. (Campo et al.Heliyon 2016, 2 (5), e00112; Gauzzi et al. Inorganica Chim. Acta 1985,104 (1), 1-7). Recent synthetic studies have demonstrated thatlow-temperature ion exchange reactions with Sn(II)-halides, e.g., SnF₂and/or SnCl₂, can provide an effective synthetic approach. Flux reactionconditions involve the use of relatively low-melting salts, e.g., metalchlorides or sulfates, as an effective medium to react metal oxides(Boltersdorf et al. CrystEngComm, 2015, 17, 2225-2241). Its use hasenabled the preparation of a growing number of new compounds whichexhibit limited stability or metastability such as Sn₂TiO₄ (O'Donnell etal. J. Electrochem. Soc. 2019, 166 (5), H3084-H3090; Boltersdorf et al.Chem. Mater. 2017, 28, 8876-8889), or in related systems such asCu₂Ta₄O₁₁ and Cu₂Nb₈O₂₁ (King et al. Cryst. Grow. Des. 2015, 15,552-558; Choi et al. ACS Nano 2013, 7(2), 1699-1708). The recentexamples with Sn(II) cations include the first high-purity syntheses ofSn₂TiO₄, representing the first known Sn(II)-titanate, as well as SnTiO₃with an ilmenite structure-type (Diehl et al. Chem. Mater. 2018, 30(24), 8932-8938). The former phase was synthesized starting from eitherK₂Ti₂O₅ or Ba₂TiO₄, e.g., Ba₂TiO₄(s)+2 SnClF(s)→Sn₂TiO₄(s)+2 BaClF(s).The exothermicity of salt formation drives the net reaction, with alarge enthalpy of formation of BaClF from SnClF of about −1041 kJ mol-1(O'Donnell et al. J. Electrochem. Soc. 2019, 166 (5), H3084-H3090).Thus, this approach leverages the exothermic formation of stable saltsto surmount the thermodynamic barriers to forming metastable compounds.

Elucidation of the underlying chemistry that determines thesynthesizability of metastable compounds currently represents a highlyactive research field. The fundamental principles and limits are notwell understood and have historically remained primarily empirical innature. One hypothesized criterion is that the synthesizability of ametastable compound can be determined based upon its excess enthalpyabove the ground state, such as within a range of ˜0.05 to 0.20 eVatom⁻¹ above the convex hull in composition space. More recently,computational investigations have demonstrated that a greater cohesiveenergy enables the synthesis of compounds with a higher metastability(Sun et al. Sci. Adv. 2016, 2 (11), e160025; Aykol et al. Sci. Adv.2018, 4, eaaq0148). Perovskite oxides represent a large family ofcompounds with relatively high cohesive energies that are a function ofthe A-site and B-site cations (Goudochnikov et al. J. Phys.: Condens.Matter 2007, 19, 176201). A tuning of the mixed A/A′-site and B/B′-sitecations in the form of solid solutions can be used as a chemical leverto manipulate their relative stability. Perovskite compounds can serveas a testbed for exploring the underlying principles of thesynthesizability of metastable phases, such as for those containingSn(II) cations. For example, the perovskite-type SnTiO₃ and SnZrO₃, aswell as the Sn(Zr_(0.5)Ti_(0.5))O₃ solid solution, are all calculated tobe highly metastable, by ˜0.4 eV atom⁻¹ to 0.5 eV atom⁻¹, with respectto decomposition to the simpler oxides or to the ilmenite structure.Prior studies have found that the highest amount of Sn(II) that can beincorporated into the A-site of any titanate or zirconate perovskite islimited to less than about 10 mol % (Suzuki et al. Phys. Rev. B—Condens.Matter Mater. Phys. 2012, 86 (6), 8-11; Suzuki et al. Jpn. J. Appl.Phys. 2013, 52 (9 PART2), 7-10).

Described herein is the substitution of the destabilizing Sn(II) cationinto the perovskite BaZrO₃, BaTiO₃, and the Ba(Zr_(1-y)Ti_(y))O₃ solidsolutions using low temperature reactions with a salt flux and yieldinghighly metastable compositions. Perovskites are obtained in bulk formwith the highest known amounts of Sn(II) cations and that push theextreme limits of metastability that can be synthesized. The compoundswere comprehensively characterized and found to exhibit cubic perovskitestructures that become increasingly metastable with both the Sn(II) andZr(IV) concentrations. Their kinetic stabilization is attributable tothe large cohesive energy of the underlying perovskite structure as wellas the low reaction temperatures and short reaction time which mitigateion diffusion and segregation. Their bandgap sizes and photocatalyticactivities for water oxidation also show promising properties for solarenergy conversion.

Experimental Methods.

Flux Synthesis of Ba(Zr_(1-y)Ti_(y))O₃ Perovskites. The BaTiO₃, BaZrO₃and the Ba(Zr_(1-y)Ti_(y))O₃ (BZT; y=0.25, 0.5, 0.75) solid solutionswere synthesized in a molten NaCl—KCl salt flux. The reactants BaCO₃(0.0055 mol-Alfa Aesar, 99.8%), TiO₂ (0.0025 mol-J. T. Baker, >99%), andZrO₂ (0.0025 mol-Beantown Chemical, 99.5%) were ground together for 20min in the desired stoichiometry with a 10% mole excess of BaCO₃. Aftermixing, an equimolar mixture of NaCl (0.05 mol) and KCl (0.05 mol) wereprepared with a salt-to-product ratio of 20:1 that was ground for 20min. The reactants were loaded into an alumina crucible and heated to1100° C. at a rate of 10° C. min⁻¹ and soaked for 24 hours beforecooling to room temperature. Products were washed multiple times indeionized water and centrifuged in order to remove any salt flux anddried overnight at 80° C.

Flux-Assisted Synthesis of (Ba_(1-x)Sn_(x))(Zr_(1-y)Ti_(y))O₃ (BSZT).The BSZT phases (y=0.0, 0.25, 0.5, 0.75, 1.0; x=0.1 to 1.0 in incrementsof 0.1) were synthesized via flux-assisted reactions using the BaTiO₃,BaZrO₃, BZT and SnClF reactants. The perovskites (0.001 mol) were groundtogether with an appropriate stoichiometric amount of SnCl₂ (Alfa Aesar,99% min) and SnF₂ (Alfa Aesar, 97.5%) under an argon atmosphere for 20min and then loaded into a fused-silica tube and placed under dynamicvacuum. The evacuated and flame-sealed tubes were then heated to 350° C.at a rate of 12° C. min⁻¹, held for 12 hours, and radiatively cooled toroom temperature. Products were thoroughly washed and centrifuged withdeionized water to remove any unreacted salt flux or side products, anddried overnight at 80° C.

Characterization. Powder diffractograms for all samples were collectedusing a Rigaku R-Axis Spider using Cu Kα radiation (λ=1.54056 Å) from asealed tube X-ray source (40 kV, 36 mA) and a curved image-platedetector. High resolution data sets for selected samples were collectedon a PANalytical Empyrean X-Ray diffractometer operating with Cu Kαradiation (45 kV, 40 mA) with a step size of 0.0131 2θ and a 300 seccount time per step. X-ray total scattering measurements for reducedpair distribution function (PDF) analysis were collected at the 11-ID-CBeam line of the Advanced Photon Source (APS) at Argonne NationalLaboratory. A wavelength of 0.1173 Å was used for 2D data collectionacquired using a Perkin-Elmer area detector. The reduction of the 2Ddata to 1D was performed using FIT2d software. The pair distributionfunction data was obtained from the 1D data using PDFgetx3 software.Neutron diffraction data were collected on the POWGEN (Beam line 11-A)time-of-flight (TOF) Diffractometer at the Spallation Neutron Source(SNS) at Oak Ridge National Laboratory during cycle run 2019-B.Polycrystalline samples (˜2 g) were sealed in cylindrical vanadiumsample cans and data were collected at 298 K and 20 K. A neutron beamwith a wavelength of 1.5 Å at 60 Hz was used with a detector ˜2.0-4.7 maway from the sample. The crystal structures were refined for both theX-ray and neutron diffraction data by the Rietveld method.

UV-vis diffuse reflectance measurements were taken using a ShimadzuUV-3600 equipped with an integrating sphere. The background was apressed barium sulfate disc. The data were transformed using theKubelka-Munk, F(R), function (Simmons et al. Appl. Opt. 1976, 15 (4),951). Since F(R) is also equal to k/s, where k and s are the absorptionand scattering coefficients, the bandgap sizes can be extracted via Taucplots of (F(R)×hv)^(n) versus photon energy for the allowed direct (n=2)and indirect (n=½) transitions. The direct and indirect bandgap energieswere determined by extrapolating the linear portion of the Tauc plots tothe baseline fit. SEM images and elemental analysis were performed usinga JOEL SM 6010LA scanning electron microscope with a 20 kV acceleratingvoltage with a secondary electron imaging detector along with a JOEL EDSSilicon Drift Detector.

Suspended Particle Photocatalysis Measurements. Photocatalytic rates formolecular oxygen were measured without the addition of a cocatalystusing similar conditions as reported previously (Boltersdorf et al. ACSCatal. 2013, 3, 2943-2953; McLamb et al. Cryst. Growth Des. 2013, 13,2322-2326). The photocatalytic rates of molecular oxygen production weremeasured using an outer-irradiation type fused-silica reaction cell witha Xe arc-lamp and photon flux of ˜200 mW cm-2. The Xe arc lamp wasequipped with an IR filter and samples were irradiated withultraviolet-visible light (λ>230 nm) and visible light (λ>400 nm).Suspensions were degassed via sonication with flowing nitrogen.Photocatalytic rates were measured in an aqueous 0.05 M AgNO₃ solution(Alfa Aesar, 99.9%). Measurements were taken every 10 min for 90 min toobtain the initial rate, and then every 30 min thereafter. Gasproduction was measured volumetrically, and the products were identifiedvia gas chromatography.

Electronic Structure Calculations. Total energy and electronic structurecalculations were performed using 4×4×4 supercells of(Ba_(1-x)Sn_(x))(Zr_(1-y)Ti_(y))O₃ using density functional theorymethods as implemented in the Vienna Ab initio Simulation Package (ver.4.6) (Kresse et al. Comput. Mater. Sci. 1996, 6 (1), 15-50; Perdew etal. Phys. Rev. Lett. 1996, 77, 3865). Calculations were performed usingPerdew-Burke-Ernzerhof functionals in the generalized gradientsapproximation using the projector augmented wave method. TheBrillouin-zone was automatically sampled using a 2×2×2 Monkhorst-Packgrid. The cubic phase of BZT and BSZT were simulated using the cubicperovskite Pm-3m space group with lattice constants determined from theexperimental values.

Decomposition energies of the Sn(II)-containing BSZT perovskites werecalculated following a previously reported procedure by Hautier et al.(Emery et al. Scient. Data 2017, 4, 170153; Hautier et al. Phys. Rev.B—Condens. Matter Mater. Phys. 2012, 85, 155028), wherein the use oftotal energy calculations have been demonstrated to accurately predictreaction energies of ternary metal oxides from their binary oxides.Total energies are calculated at 0 K using density-functional theorymethods and then used to accurately calculate the overall reactionenergy. As all reactants and products are solids, entropic contributionsare assumed negligible at room temperature. For example, thedecomposition of the Sn(II)-free oxides to their constituent binaryoxides, i.e., Ba(Zr_(1-y)Ti_(y))O₃→BaO+(1−y) ZrO₂+y TiO₂, werecalculated to be thermodynamically unfavorable (ΔE_(deomp) of up to ˜0.3eV atom⁻¹). The reaction energy of decomposition of the metastableSn(II)-containing perovskites were calculated according to the observeddecomposition products, as described below. In nearly all cases theSn(II)-containing perovskites decomposed via the formation of SnO andstoichiometric amounts of Ba(Zr_(1-y)Ti_(y))O₃, TiO₂ and ZrO₂. Totalenergies of the binary oxides and the specific BZT/BSZT compositionswere calculated, as well as taken or cross-checked with the Open QuantumMaterials Database (Saal et al. JOM 2013, 65, 1501-1509).

Results and Discussion.

Synthesis and Structural Characterization. Low temperature flux-assistedreactions were investigated to prepare Sn(II)-containing perovskitesstarting from the barium perovskites, i.e., Ba(Zr_(1-y)Ti_(y))O₃+xSnClF→(Ba_(1-x)Sn_(x))(Zr_(1-y)Ti_(y))O₃+x BaClF. While pure BaTiO₃ istetragonal, all other BZT compositions in this study (i.e., ≥25% Zr,y=0.75) crystallize in the cubic polymorph at room temperature. TheBa(Zr_(1-y)Ti_(y))O₃ compositions were reacted with SnClF to produce(Ba_(1-x)Sn_(x))(Zr_(1-y)Ti_(y))O₃ (BSZT) in increasing increments of0.1 (x=0.0 to 1.0). Bulk powder XRD data for each composition are shownin FIG. 26 to FIG. 30 . Representative powder XRD data of unwashed BSZTshows the formation of increasing amounts of BaClF, shown in FIG. 31 .The highest percentage of Sn(II) substitution into BaTiO₃, i.e.,(Ba_(1-x)Sn_(x))TiO₃, that maintained the perovskite structure was only˜10%, or x=0.1. Higher amounts of Sn(II) substitution resulted in theformation of the ilmenite-type SnTiO₃ in increasing amounts. With asmall increase of 25% Zr on the B-site, i.e., Ba(Zr_(0.25)Ti_(0.75))O₃,closer to ˜40% Sn(II) could be substituted before the formation of theilmenite-type SnTiO₃ phase. Starting from pure BaZrO₃, the maximumamount of Sn(II) substitution in (Ba_(1-x)Sn_(x))ZrO₃ is furthersignificantly increased to ˜50% to 60%, or x=0.5 to 0.6. This representsthe highest Sn(II) concentration ever reported on the A-site for aperovskite-type structure. No evidence is found for an ilmenite-type‘SnZrO₃’ composition at higher amounts. Instead, higher amounts ofSn(II) in the loaded reaction stoichiometry result in increasingdiffraction peaks for a SnO impurity.

A high amount of Sn(II) substitution was also possible in the 50:50BaZrO₃—BaTiO₃ solid solution, i.e., Ba(Zr_(0.5)Ti_(0.5))O₃, with up to˜60% Sn(II) cations and the maintenance of the cubic perovskitestructure. The powder XRD data show a minor amount of ZrO₂ impurity inall samples beyond ˜30% Sn(II) concentration. However, the EDS data ofthe washed samples (FIG. 36 and FIG. 37 ), listed in Table 1, show thatup to ˜60% Sn(II) can be incorporated into the structure. Thecompositional trends in the EDS data are also consistent with the loadedstoichiometries of each reaction, within a standard deviation of ˜5%. Inorder to probe these structures in more detail, high resolution X-raydiffraction data were collected for Ba(Zr_(0.5)Ti_(0.5))O₃ and for itscompositions with 20%, 40% and 60% Sn(II) cations to perform Rietveldrefinements, FIG. 32 -FIG. 35 . High resolution neutron diffraction datawere also collected for the latter two compositions for Rietveldanalysis, FIG. 1 -FIG. 4 . Results of the Rietveld refinements of the(Ba_(1-x)Sn_(x))(Zr_(0.5)Ti_(0.5))O₃ compositions, Table 2, most closelymatched with a cubic perovskite structure, with weighted residuals of ˜3to 6%.

TABLE 1 Selected results from Energy Dispersive Spectroscopy (EDS) datataken on the BSZT phases. Composition Ba [mol %] Sn [mol %] x =Ba_(0.8)Sn_(0.2)Zr_(0.25)Ti_(0.75)O₃ 22.98  5.52 0.19Ba_(0.8)Sn_(0.2)Zr_(0.5)Ti_(0.5)O₃ 24.60  4.96 0.17Ba_(0.6)Sn_(0.4)Zr_(0.5)Ti_(0.5)O₃ 17.32 10.84 0.38Ba_(0.4)Sn_(0.6)Zr_(0.5)Ti_(0.5)O₃ 12.33 15.20 0.55Ba_(0.8)Sn_(0.2)Zr_(0.75)Ti_(0.25)O₃ 23.34  5.68 0.20Ba_(0.8)Sn_(0.2)ZrO₃ 10.15  2.38 0.19 Ba_(0.6)Sn_(0.4)ZrO₃ 13.58  7.070.34

TABLE 2 Results of Rietveld refinements of neutron and X-ray diffractiondata at room temperature for selected compositions of the(Ba_(1−x)Sn_(x))(Zr_(0.5)Ti_(0.5))O₃ solid solution. LoadedBaZr_(0.5)Ti_(0.5)O₃ Ba_(0.8)Sn_(0.2)Zr_(0.5)Ti_(0.5)O₃Ba_(0.6)Sn_(0.4)Zr_(0.5)Ti_(0.5)O₃ Ba_(0.4)Sn_(0.6)Zr_(0.5)Ti_(0.5)O₃Composition (0% Sn) (20% Sn) (40% Sn) (60% Sn) Radiation X-ray X-rayX-ray Neutron X-Ray Neutron Lattice 4.095(1) 4.097(0) 4.095(9) 4.0922(8)4.093(7) 4.090(8) Constant [Å] R(w) [%] 4.67 3.55 3.25 5.69 3.67  5.90 Ba fraction 1.0*  0.82(3)  0.61(9)  0.58(8) 0.400* 0.400* Sn fraction0.0*  0.17(7)  0.38(1)  0.41(2) 0.600* 0.600* Zr fraction  0.47(3) 0.44(5)  0.47(7)  0.45(1)  0.47(0)  0.48(5) Ti fraction  0.52(7) 0.55(5)  0.52(3)  0.54(9)  0.53(0)  0.51(5) *Value was fixed duringrefinement.

The lattice constant was found to slightly contract with Sn(II)substitution and ranged from 4.095(1) Å to 4.090(8) Å. In addition, therefined elemental distributions of Ba/Sn cations on the A-site and theZr/Ti cations on the B-site were consistent with the loaded reactionstoichiometries. Neutron diffraction data were also taken at 20 K forthe 40% and 60% Sn(II) perovskites in order to probe whether alow-temperature phase transition occurs, similar to that known forBaTiO₃ and the Ba(Zr_(1-y)Ti_(y))O₃ solid solution. Both compositionsremained well matched to the cubic perovskite structure at lowtemperatures, FIG. 3 and FIG. 4 and Table 3, with only a smallcontraction of the lattice constant.

TABLE 3 Selected Rietveld refinement results of neutron diffraction dataat 20K. Ba_(0.6)Sn_(0.4)Zr_(0.5)Ti_(0.5)O₃Ba_(0.4)Sn_(0.6)Zr_(0.5)Ti_(0.5)O₃ Lattice Constant [Å] 4.0871(4)4.0905(7) Refined Weighted 7.030 7.629 Residuals [%] Refined Ba  0.600* 0.400* Refined Sn  0.400*  0.600* Refined Zr  0.45(3)  0.51(5) RefinedTi  0.54(7)  0.485(1) *Value was fixed during refinement.

The BSZT compositions all surprisingly indicated the lack of astereoactive lone pair on the Sn(II) cation. The Sn(II) cation canundergo an atomic displacement similar to the isoelectronic Pb(II)cation in the well-known PZT compositions. All previously reportedcrystal structures of binary and ternary Sn(II)-containing oxides haveshown the presence of a stereoactive lone pair. In order to investigatethe local structures, total X-ray scattering data were collected and thepair distribution functions (PDFs) were calculated for representativecompositions (Proffen et al. Zeitschriftfur Krist. 2004, 219 (3),130-135; Aksel et al. Phys. Rev. B—Condens. Matter Mater. Phys. 2013, 87(10), 1-10). These data are shown in FIG. 5 , FIG. 6 , and FIG. 8 forBa(Zr_(0.5)Ti_(0.5))O₃ with 0%, 20% and 60% Sn(II) substitution,respectively, and in FIG. 7 for Ba(Zr_(0.25)Ti_(0.75))O₃ with 20% Sn(II)substitution. The refinement results confirmed the long-range structuresand contracting unit cell dimensions of these cubic perovskitestructures. Shown in FIG. 38 -FIG. 39 , the calculated pair distributionfunctions at small distances (r<8.0 Å) show that all interatomicdistances are consistent with the cubic perovskite model. However, thelocal structure (r<3.0 Å) for the 60% Sn(II) perovskite indicated somesmall deviations from the ideal cubic symmetry, FIG. 8 , that has so farnot been adequately modeled in the refinements as it requires more modelcomplexity. Preliminary results show that the introduction of apseudocubic structure, which allows for small distortions to be modeledin the Sn(II) position along the [001] and [111] directions, can improvethe Rietveld refinement results for the 60% Sn composition when comparedwith the cubic lattice structure.

The stereoactivity of the post-transition metal oxides has beenexplained by the Revised Lone Pair Model (RLP) previously (Walsh et al.Chem. Soc. Rev. 2011, 40 (9), 4455-4463). In brief, metal cations withelectron configurations d¹⁰ s²p⁰ in groups 13-16 can exhibitstereoactive lone pairs arising from the mixing of the unoccupied cationp-orbitals with the anti-bonding cation s and anion p states. Stronglone-pair activity occurs when the cation s and anion p states are closein energy, such as for Sn(II) cations bonded to oxygen. Additionally,the net electronic stabilization must be greater than the energeticpenalty from the decrease in coordination. Based on the Revised LonePair model, the lack of lone pair activity appears unusual. However, themixed A/A′-site of BSZT contains both Ba(II) and Sn(II), of which onlythe latter has the requisite electronic configuration to favor astructural distortion. A greater Sn(II) substitution on the A-site wouldlead to a larger concerted electronic driving force to give thedistorted perovskite structure, as predicted for SnTiO₃ orSn(Zr_(0.5)Ti_(0.5))O₃. The lack of a lone-pair can thus be attributedto the energetic penalty for the decrease in coordination of both Ba andSn(II) being greater than the electronic stabilization afforded toSn(II) in a distorted environment.

Particle Sizes and Morphologies. Scanning electron microscope (SEM)images were taken to measure the particle sizes and morphologies of theperovskite products both before and after the substitution of the Sn(II)cations. This was used to probe for evidence of whether the perovskitestructure had melted and re-crystallized, or alternatively, if arelatively ‘soft’ Sn(II)-exchange had occurred to give the productswithout it melting. Shown in FIG. 9 -FIG. 16 are the SEM images takenfor the (Ba_(1-x)Sn_(x))(Zr_(0.5)Ti_(0.5))O₃ family of compounds, for0%, 20%, 40%, and 60% Sn(II) substitution. The crystallite particles ofthe unsubstituted Ba(Zr_(0.5)Ti_(0.5))O₃, FIG. 9 and FIG. 10 , exhibitedan almost cubic-shaped morphology with smooth surfaces and sizes rangingfrom ˜0.5 to 2 μm. The perovskite with 20% Sn substitution, FIG. 11 andFIG. 12 , showed the same general particle sizes but with slightly moreirregular morphologies with roughened surfaces. The perovskite sampleswith 40% and 60% Sn(II) substitution showed the same trend.

Significantly, no evidence was found for particle coarsening oragglomerating that would indicate the melting or dissolution of theBa(Zr_(0.5)Ti_(0.5))O₃ particles during the substitution of the Sn(II)cations. The incorporation of Sn(II) cations can even be achieved tosome extent without the breakup of the particles, up to about 20%Sn(II). However, the addition of larger amounts of Sn(II) significantlyfractures the particles owing to the difference in ionic size betweenthe Ba(II) and Sn(II) cations, which have crystal radii of ˜1.35 Å and˜0.95 Å, respectively. As the crystal radius of 12-fold coordinateSn(II) is unknown, the preceding values for 6-fold coordination are usedonly as a common reference point to compare the relative crystal radiiof Ba and Sn(II). The trends in the measured Ba:Sn molar ratios fromenergy dispersive X-ray spectroscopy were consistent with the results ofthe structure refinements and the loaded reaction stoichiometries, Table1.

Thermodynamic Calculations of Stability. To probe the stability of theperovskite oxides, total energies of each of the compositions wereobtained from DFT results available in the Open Quantum MaterialsDatabases. Some solid solutions were also calculated for consistencyusing the VASP software package. Prior studies by Hautier et al. havedemonstrated that total energies can be used to determine the reactionenergies for the formation of metal oxides at 0 K (Hautier et al. Phys.Rev. B—Condens. Matter Mater. Phys. 2012, 85, 155028). The calculatedreaction energies have been shown to be accurate within a mean deviationof close to zero and a standard deviation of only ˜24 meV atom⁻¹, i.e.,much smaller than the reaction energies. The reaction energies, e.g.,AO+BO₂→ABO₃, indicate the extent of metastability (ΔE_(decomp)>0) of theperovskite toward decomposition to a more stable polymorph or the binaryoxides. Stabilities were estimated as a function of both A/A′- andB/B′-site compositions.

The decomposition pathways calculated for the(Ba_(1-x)Sn_(x))(Zr_(1-y)Ti_(y))O₃ (BSZT) perovskites were based uponthe experimentally observed products at each composition. For example,both pure Sn(II)-based perovskites are highly thermodynamically unstablewith respect to decomposition to the binary oxides, e.g.,SnZrO₃→SnO+ZrO₂ by a significant ˜2.3 eV formula⁻¹ (˜0.46 eV atom⁻¹). Bycomparison, BaZrO₃ is thermodynamically stable with respect todecomposition to the constituent binary oxides. For a mixedBa(II)/Sn(II) solid solution the decomposition is calculated accordingto the following reaction: 2 (Ba_(0.5)Sn_(0.5))ZrO₃→BaZrO₃+SnO+ZrO₂. Thedecomposition products are consistent with the experimental productdistributions, as shown for example in FIG. 40 and FIG. 41 . In a mixedBa(II)/Sn(II) and Ti(IV)/Zr(IV) solid solution of BSZT, thedecomposition reaction proceeds by the formation of a mixture of SnO andZrO₂/TiO₂.

The decomposition energies of the reactions were calculated and plottedin FIG. 17 as a function of the A/A′-site (Ba/Sn; x-axis) and B/B′-site(Zr/Ti; y-axis) compositions in the BaTiO₃—BaZrO₃—SnTiO₃—SnZrO₃ system.All 100% Sn(II)-based perovskites are thermodynamically unstable, e.g.,SnTiO₃ is thermodynamically unstable with respect to decomposition toSnO and TiO₂ by a significant ˜2.0 eV formula⁻¹ (˜0.40 eV atom⁻¹).Starting from the thermodynamically stable BaTiO₃, an increasingsubstitution of Sn(II) into the structure can be modeled as the solidsolution (Ba_(1-x)Sn_(x))TiO₃ with increasing x, shown in FIG. 17 (upperright x-axis). The solid solution rapidly becomes unstable with respectto decomposition beyond x ˜0.15, or ˜15% Sn(II) cations, in agreementwith prior synthetic studies using high temperature conditions that havefound ˜10% or less of Sn(II) can be incorporated into titanateperovskites. Similar results are found for the zirconate analogue, i.e.,(Ba_(1-x)Sn_(x))ZrO₃ in FIG. 17 (x-axis; lower left), which is predictedto be metastable beyond ˜15% Sn(II) cations. Consistent results arefound for Sn(II)-substitution across the entire mixed-Ti/Zr compositionrange of the (Ba_(1-x)Sn_(x))(Zr_(1-y)Ti_(y))O₃ solid solution. At allcompositions, a higher Sn(II) content leads to a rapid decrease instability with a nearly linear negative slope in the perovskiteformation energy of ˜0.5 eV formula⁻¹.

An enhanced synthesizability of metastable perovskites containing Sn(II)cations is found with an increasing Zr substitution on the B-site,although these compositions are more highly metastable. With 0% Zr,i.e., BaTiO₃, only ˜10% Sn(II) could be substituted before the productconverted to the more stable ilmenite structure type. However, up to 50%to 60% Sn(II) substitution could be achieved in the perovskite structurewhen Zr(IV) cations were substituted for Ti(IV) cations on the B-site,leading to the metastable (Ba_(0.5)Sn_(0.5))ZrO₃ or(Ba_(0.4)Sn_(0.6))(Ti_(0.5)Zr_(0.5))O₃. These compositions occur in theareas of high metastability, FIG. 17 , and are highly unstable withrespect to decomposition to the binary oxides by ˜0.27 eV atom⁻¹ and˜0.25 eV atom⁻¹, respectively. By comparison, it has typically beenconsidered that an excess free energy above some empirically-definedlimit, e.g., ranging from −0.05 to 0.15 eV atom⁻¹, will render ametastable phase not synthesizable (Sun et al. Sci. Adv. 2016, 2 (11),e160025; Aykol et al. Sci. Adv. 2018, 4, eaaq0148). TheSn(II)-substitution obtained by the low-temperature flux reactionsgreatly exceeds the thermodynamic limits of stability with ametastability that has not been found using high temperature syntheticmethods.

Possible explanations for the successful synthesis of the highlymetastable BSZT compositions are the configurational entropy and/or thekinetic stabilization provided by the high cohesive energy of theunderlying perovskite network. As has been shown for entropy-stabilizedoxides and alloys, enhanced phase stability can result when a largenumber of different elements are mixed and disordered over the samecrystallographic sites (Yeh et al. Adv. Eng. Mater. 2004, 6 (5),299-303; Rost et al. Nat. Commun. 2015, 6, 8485). For BSZT, which hastwo sites mixed with two metal cations, the calculated S_(max) is onlyon the order of ˜5.0×10⁻⁵ eV K⁻¹, or ˜0.015 eV at room temperature. Thisis significantly smaller than the calculated decomposition energies,showing this is too small to be responsible for the stabilization ofBSZT. Furthermore, entropy stabilized solids become more stable withincreasing temperature rather than decompose as observed for BSZT. Whilethe (Ba_(0.7)Sn_(0.3))(Zr_(0.5)Ti_(0.5))O₃ composition can besuccessfully synthesized, exchange reactions performed at highertemperatures for longer time clearly results in decomposition, FIG. 40 .Additionally, heating of the BSZT compositions with >10% Sn(II) cationsat higher temperatures leads to decomposition, FIG. 41 .

Large-scale studies have shown that metastable phases are morefrequently found, i.e., synthesizable, when they have higher cohesiveenergies (Sun et al. Sci. Adv. 2016, 2 (11), e160025; Aykol et al. Sci.Adv. 2018, 4, eaaq0148). These findings indicate that stronger bonds canbe more capable of ‘locking in’ energetically unfavorable atomicarrangements. Furthermore, the likelihood of a ground state of ametastable phase being phase separated rather than polymorphic increaseswith the number of elements, with inhibition of the atomic diffusion andsegregation providing a kinetic barrier for decomposition to morethermodynamically favored products (Sun et al. Sci. Adv. 2016, 2 (11),e160025). Perovskite oxides have been found to exhibit relatively highcohesive energies, especially for zirconates (Goudochnikov et al. J.Phys.: Condens. Matter 2007, 19, 176201), and can therefore kineticallystabilize against decomposition by inhibiting significant cation andanion diffusion. The above factors help to understand the high amount ofSn(II) that can be substituted under these reaction conditions intodifferent compositions of the Ba(Zr_(1-y)Ti_(y))O₃ perovskite. Thesynthesis of metastable (Ba_(1-x)Sn_(x))(Zr_(1-y)Ti_(y))O₃ (BSZT), witha positive free energy of formation, is driven by the larger negativefree energy of formation of BaClF in the reaction. The low reactiontemperature, short reaction time, and high cohesive energy of the BZTphases inhibit long-range ion diffusion. When comparing BaTiO₃ andBaZrO₃, the former readily converts to the ilmenite-structure type withthe substitution of >10% Sn(II) cations of the same composition withoutthe need for significant ion diffusion. By contrast, the ilmenitestructure is not stable for the zirconate perovskite and must thereforedecompose by significant cation diffusion and segregation into simplerbinary oxides. As compared to BaTiO₃, the BaZrO₃ perovskite also has ahigher cohesive energy (−41.43 eV versus −39.69 eV) and a significantlyhigher melting point (2,700° C. versus 1,625° C.). As a result, BaZrO₃can incorporate a much higher amount of ˜50-60% Sn(II) cations with ahigh metastability before the onset of decomposition.

A high metastability is also achieved for the mixed B-site solidsolution of 50% Zr(IV) and 50% Ti(IV) cations, i.e., starting from theBa(Zr_(0.5)Ti_(0.5))O₃ perovskite. In this perovskite up to ˜60% Sn(II)can be attained, i.e., (Ba_(0.4)Sn_(0.6))(Zr_(0.5)Ti_(0.5))O₃. Itsdecomposition is inhibited as significant ion diffusion is required fordecomposition to occur to give the binary oxides ZrO₂ and SnO. TheBa(Zr_(0.5)Ti_(0.5))O₃ solid solution is the composition where both theZr(IV) and Ti(IV) are the most diluted in the perovskite lattice, andconsequently, the greatest ion diffusion is required for decomposition.For example, the synthesis of MS₂ (M=Fe, Co, Ni) has similarly shownthat crystalline metastable intermediates are observed during thereaction of Na₂S₂ with MCl₂ that are trapped owing to the limited iondiffusion achieved under low temperature solid-state reaction conditionsin a similar fashion to BSZT (Martinolich et al. J. Am. Chem. Soc. 2016,138 (34), 11031-11037). This suggests that an effective approach for thesynthesis of metastable phases is the dilution of multiple differentcations over equivalent crystallographic sites, requiring maximal iondiffusion for their decomposition.

Optical Properties and Electronic Structure. Metal oxides containing theSn(II) cation are under intense investigation as small bandgapsemiconductors. Optical absorption measurements were taken to probe howthe increasing Sn(II) substitution impacts the band gap. The direct andindirect bandgap energies are plotted together in FIG. 18 -FIG. 20 as afunction of the mixed A/A′-site (Ba/Sn; x-axis) and B/B′-site (Zr/Ti;y-axis) stoichiometries. All compositions show a lowest energy indirectbandgap transition spanning a wide range from ˜3.90 eV for BaZrO₃ to˜1.95 eV for (Ba_(0.7)Sn_(0.3))(Zr_(0.25)Ti_(0.75))O₃, with direct bandgaps for each composition that is ˜0.2 eV to 0.8 eV higher in energy.The band gap is generally found to decrease with increasing Sn(II) andTi(IV) compositions, as labeled by the red areas in FIG. 18 . As theSn(II) concentration increases, an absorption edge at lower energy formsand grows as a result of the increasing density of the Sn(II) states inthe valence band. These results are consistent with prior research onsolid solutions with tunable chemical compositions (Palasyuk et al.Inorg. Chem. 2010, 49 (22), 10571-10578; Boltersdorf et al. J. Phys.Chem. C 2016, 120 (34), 19175-19188). Compositions with the highestamounts of Sn(II) cations exhibit the smallest band gaps, e.g., 1.95 eVfor (Ba_(0.7)Sn_(0.3))(Zr_(0.25)Ti_(0.75))O₃, 2.14 eV for(Ba_(0.4)Sn_(0.6))(Zr_(0.5)Ti_(0.5))O₃, and 2.40 eV for(Ba_(0.7)Sn_(0.3))(Zr_(0.75)Ti_(0.25))O₃. The regions of the BSZTcomposition space with the smallest bandgap sizes also correspond to theareas of highest metastability in FIG. 17 . The ZrO₂ impurity found insome samples exhibits a band gap of >5.0 eV, significantly higher inenergy than found for the BSZT phases. These results show an underlyingrelationship between high metastability and the formation of thesmallest band gaps.

The dependence of the bandgap size on the BSZT composition can be fittedto the standard bowing equation (Wu et al. Solid St. Comm. 2003, 127,411-414):E _(g) ^(BSZT)(x)=E _(g) ¹ ×+E _(g) ²(1−x)-bx(1−x)wherein E_(g) ⁻¹ and E_(g) ² are the band gaps of the endpointcompositions, x is the mole fraction of each, and b is the bowingparameter. Starting from −10% Sn(II) in each BSZT composition, anincreasing Sn(II) substitution could be well-fitted to a bowingparameter of 0.45 eV. The largest change in the indirect band gapoccurred with the increase from 0% to 10% Sn(II) cations, decreasing theband gap by a consistent ˜0.75 to 0.9 eV for all compositions. Forexample, the 3.30 eV bandgap size of Ba(Zr_(0.5)Ti_(0.5))O₃ wasdecreased to 2.54 eV with the introduction of only 10% Sn(II) cations.The bowing parameter value, fitted from 10% to 60% Sn(II) cations,represents the extent of band widening and dispersion that occurs withincreasing amounts of —O—Sn—O—Sn—O connectivity within the structure.The band dispersion also has a significant impact on the energeticseparation between the indirect and direct bandgap transitions thatincreases with the Sn(II) and Ti(IV) cations, shown in FIG. 20 and FIG.42 -FIG. 51 , with the valence band widening having a predominant effecton the indirect transition.

Electronic structure calculations were performed in order to probe theorigins of the changes in the bandgap size with increasing Sn(II)substitution, given in FIG. 52 -FIG. 53 . For Ba(Zr_(0.5)Ti_(0.5))O₃,the band gap is primarily set by the energetic distance between the Ti3d- and O 2p-based states, with the Zr 4d orbitals located at higherenergies. After substitution of 60% Sn(II) cations, the valence band isnow composed of strongly interacting Sn 5 s and O 2p states, with ashift of the valence band edge to higher energies. These results areconsistent with prior electronic structure investigations ofSn(II)-containing oxides, wherein the Sn 5 s orbitals interact with theO 2p orbitals at the valence band edge and result in a smaller band gap(Noureldine et al. Catal. Sci. Technol. 2016, 6 (21), 7656-7670;O'Donnell et al. J. Electrochem. Soc. 2019, 166 (5), H3084-H3090). Asthe concentration of Sn(II) increases, the Sn 5 s contributions in thevalence band increases. This is a result of the extended—O—Sn—O—Sn—O-network that is formed with greater Sn(II) substitution,and which increases the Sn—O antibonding interactions.

Suspended Particle Photocatalysis. Prior experimental and computationalstudies have predicted that Sn(II)-containing oxides frequently havefavorable band energetics for efficient photocatalysis under sunlight(Noureldine et al. Catal. Sci. Technol. 2016, 6 (21), 7656-7670;O'Donnell et al. J. Electrochem. Soc. 2019, 166 (5), H3084-H3090;Boltersdorf et al. Chem. Mater. 2017, 28, 8876-8889; Emery et al.Scient. Data 2017, 4, 170153; Saal et al. JOM 2013, 65, 1501-1509;Nishiro et al. Chem Commun. 2017, 53, 629-632). For example, previousphotocatalytic measurements on Sn₂TiO₄, with a band gap of only ˜1.55eV, showed high activity for molecular oxygen evolution with an apparentquantum yield of ˜1.0% under 420 nm irradiation (O'Donnell et al. J.Electrochem. Soc. 2019, 166 (5), H3084-H3090; Boltersdorf et al. Chem.Mater. 2017, 28, 8876-8889). Extended —O—Sn—O—Sn—O connectivity canresult in highly disperse valence bands, yielding low carrier effectivemasses and high carrier mobilities (Ha et al. J. Mater. Chem. C 2017, 5(23), 5772-5779).

Photocatalytic activities across the full range of synthesizable(Ba_(1-x)Sn_(x))(Zr_(1-y)Ti_(y))O₃ (BSZT) powders were measured formolecular oxygen evolution. These rates are plotted collectively in FIG.21 -FIG. 23 as a function of the mixed A-site Ba/Sn (x) and B-site Zr/Ti(y) compositions. Photocatalytic rates were taken under combinedultraviolet and visible (UV+Vis) light (λ>230 nm) or under onlyvisible-light (λ>400 nm) irradiation, FIG. 21 and FIG. 22 ,respectively, and Table 4. Bandgap transitions of the BZT phases, i.e.,Ba(Zr_(1-y)Ti_(y))O₃, all occur in the ultraviolet energies of >3.2 eV.Accordingly, these perovskites all showed little to no activity undervisible-light irradiation, but relatively high activity under UV+Vislight of ˜170 to 210 μmol O₂ h⁻¹g⁻¹. In contrast, the substitutionof >10% Sn(II) cations in the BSZT phases, i.e.,(Ba_(1-x)Sn_(x))(Zr_(1-y)Ti_(y))O₃, resulted in visible-light band gapsand significantly higher activities under both ultraviolet andvisible-light irradiation. The higher rates are attributable in part tothe absorption of a larger fraction of visible-light wavelengths. Undercombined ultraviolet-visible or visible-only irradiation, the highestmeasured photocatalytic activities peaked at around the(Ba_(0.6)Sn_(0.4))(Zr_(0.5)Ti_(0.5))O₃ composition with rates of ˜408μmol O₂ h⁻¹g⁻¹ and ˜216 μmol O₂ h⁻¹g⁻¹, respectively. Conservativeestimates of the apparent quantum yields (AQY) give lower limits of˜0.51% (230 nm<λ<564 nm) and ˜0.39% (400 nm<λ<564 nm) for thiscomposition. The bubbles of molecular oxygen that evolved very rapidlyadhered strongly to the particles' surfaces, significantly slowing theapparent reaction rates that were measured volumetrically. This was aresult of the particles becoming increasingly hydrophobic withincreasing Sn(II) substitution.

TABLE 4 Photocatalytic Rates of BSZT Compounds for Molecular OxygenEvolution Under UV + Vis and Visible-Light Irradiation. UV + Vis Vis %Composition [μmol O₂ h⁻¹g⁻¹] [μmol O₂ h⁻¹g⁻¹] VisibleBaZr_(0.25)Ti_(0.75)O₃ 211  50  24 Ba_(0.9)Sn_(0.1)Zr_(0.25)Ti_(0.75)O₃232 166  72 Ba_(0.8)Sn_(0.2)Zr_(0.25)Ti_(0.75)O₃  28 188  66Ba_(0.7)Sn_(0.3)Zr_(0.25)Ti_(0.75)O₃ 197 188  95 BaZr_(0.5)Ti_(0.5)O₃173  95  55 Ba_(0.9)Sn_(0.1)Zr_(0.5)Ti_(0.5)O₃ 311 106  34Ba_(0.8)Sn_(0.2)Zr_(0.5)Ti_(0.5)O₃ 293 205  70Ba_(0.7)Sn_(0.3)Zr_(0.5)Ti_(0.5)O₃ 311 184  59Ba_(0.6)Sn_(0.4)Zr_(0.5)Ti_(0.5)O₃ 408 216  53Ba_(0.5)Sn_(0.5)Zr_(0.5)Ti_(0.5)O₃ 314 188  60Ba_(0.4)Sn_(0.6)Zr_(0.5)Ti_(0.5)O₃ 265 183  69 BaZr_(0.75)Ti_(0.25)O₃200  40  20 Ba_(0.9)Sn_(0.1)Zr_(0.75)Ti_(0.25)O₃ 152 180 120Ba_(0.8)Sn_(0.2)Zr_(0.75)Ti_(0.25)O₃ 167 148  89Ba_(0.7)Sn_(0.3)Zr_(0.75)Ti_(0.25)O₃ 136 165 121

The Sn(II)-containing BSZT compositions all showed similar highphotocatalytic rates for molecular oxygen production under visible-lightirradiation, FIG. 22 , while there was a detectable peaking in the ratesat x=0.4 and y=0.5 under combined ultraviolet-visible irradiation, FIG.21 . In this case the electrons are excited across the band gap into arange of relatively lower to higher energies within the conduction band.As the conduction band is composed of a disordered distribution of theempty d-orbitals of the Ti(IV) and Zr(IV) cations, it might be assumedthat a significant amount of local trapping of the excited electronscould predominate. Recent results have suggested that photocatalyticactivities can peak beyond the percolation threshold of disordered solidsolutions (Zoellner et al. Inorg. Chem. 2019, 58, 6845), wherebyextended diffusion pathways ‘open up’ across the extended crystallinestructure at specific compositions. The percolation threshold is definedby the concentration at which the charged carriers are no longer trappedin isolated, low-energy defects, but instead coalesce to form a new bandwith an accompanying delocalization of excited carriers (Kirkpatrick.Rev. Mod. Phys. 1973, 45, 574). An example of a two-dimensionalpercolation network is shown schematically in FIG. 24 -FIG. 25 for amixed TiO₆/ZrO₆ solid solution where the octahedra have 4-foldconnectivity. The percolation pathways form the conduction band edge,owing to the lower-energy Ti d-orbitals relative to the Zr d-orbitals.For a two-dimensional network, the percolation threshold is reached at50% Ti(IV) substitution, shown as white squares in FIG. 24 , while it isnot reached for only 30% Ti(IV) substitution, FIG. 25 . For the former,the thermalization of the excited charge carriers to the band edges thusleads to delocalization throughout the percolation network, such asreported previously for the Nb(V)/Ta(V) cation solid solution (Zoellneret al. Inorg. Chem. 2019, 58, 6845). Similarly, the holes willthermalize to the valence band edge composed of Sn-5 s and O-2p basedstates and will become delocalized at Sn(II) concentrations that exceedthe percolation threshold.

The percolation thresholds for both the A-site (Ba/Sn) and B-site(Ti/Zr) cations, P_(a) and P_(b) respectively, can be calculated towithin a few percent for the three-dimensional cubic perovskitestructure using the equation by Shante and Kirkpatrick (Shante et al.Adv. Phys. 1971, 20(85), 325-357):

${z \times p_{c}} = \frac{d}{d - 1}$where z is the coordination number, p_(c) is the percolation threshold,and d is the lattice dimensionality. The percolation threshold is theminimum concentration of a cation to form a complete path of adjacentsites, i.e., —O—Ti—O—Ti—O— or —O—Sn—O—Sn—O—, extending to the particles'surfaces. For the A-site Sn(II) cations, with 12-fold coordination and adimensionality of 3, the percolation threshold corresponds to ap_(c)(Sn) of only ˜12.5%, and for the B-site Ti(IV) cations (z=6, d=3)this occurs at a p_(c)(Ti) of ˜25%. Thus, all compositions with >12.5%Sn(II) cations have extended —O—Sn—O—Sn—O connectivity for diffusionpathways of the charge carriers to reach the surfaces. This Sn(II)concentration represents the threshold at which higher visible-lightactivity is observed across the entire range of BSZT compositions, asfound in the red-shaded region in FIG. 22 , consistent with therelationship between percolation theory, charge-carrier delocalization,and photocatalytic activity. For the conduction band states, allcompositions with >25% Ti(IV) cations have extended —O—Ti—O—Ti—Oconnectivity to provide percolation pathways for excited electrons. Thisis consistent with the much lower ultraviolet-visible photocatalyticrates for all perovskites with 25% or less Ti(IV) cations, as found inthe blue-colored regions of FIG. 21 . In this compositional region, theconduction electrons are more localized and have a higher probabilityfor recombination rather than reaching the particles' surfaces to drivewater oxidation. In the combined ultraviolet-visible photocatalyticdata, FIG. 21 , the peak in the highest photocatalytic rates is foundfor compositions with →25% Ti(IV) cations and >20% Sn(II) cations. Thispeak occurs under irradiation conditions where charge separation anddiffusion have a major impact on photocatalytic rates, rather thansimply a result of the smaller band gaps.

It is notable that the photocatalytic rates and apparent quantum yieldsof the BSZT perovskites are comparable to those initially reported forwhat is currently the best oxygen-evolving photocatalyst, i.e., BiVO₄ of˜100 μmol O₂ h⁻¹g⁻¹ and an AQY=0.3% (Kato et al. Chem. Lett. 2004, 33,1348-1349). However, the bandgap sizes of the BSZT perovskites aresmaller than BiVO₄ by about −0.4 to 0.5 eV and can absorb a largerfraction of sunlight. Accordingly, optimization of photocatalyticreaction conditions, including surface cocatalysts and film processingof the BSZT phases, can provide higher attainable rates and AQY's.

CONCLUSIONS

Flux-assisted reaction conditions were used to synthesize the highestknown amounts of Sn(II) cations in a perovskite,(Ba_(1-x)Sn_(x))(Zr_(1-y)Ti_(y))O₃, consisting of mixed A-siteSn(II)/Ba(II) cations and B-site Ti(IV)/Zr(IV) cations in astatistically disordered distribution. The highest attainable Sn(II)substitutions were found for the Zr(IV)-richer compositions, of up to˜60% Sn(II) in (Ba_(0.4)Sn_(0.6))(Zr_(0.5)Ti_(0.5))O₃ or ˜50-60% Sn(II)in (Ba_(0.4)Sn_(0.6))ZrO₃. These represented the most metastableperovskites that could be synthesized, with remarkably high reactionenergies for decomposition of ˜0.25 to 0.27 eV atom⁻¹. Theirsynthesizability is shown to be possible via the large cohesive energyof the underlying perovskite structure that limits the diffusion of ionsrequired for decomposition to simpler oxides. The optical bandgap sizedecreased from −3.90 eV to ˜1.95 eV with higher Sn(II) and Ti(IV)compositions, in correlation with the compositions showing the highestmetastability. The BSZT powders exhibited high photocatalytic ratesunder ultraviolet-visible or visible-light irradiation for molecularoxygen evolution that peaked at ˜408 μmol O₂ h⁻¹g⁻¹ and ˜216 μmol O₂h⁻¹g⁻¹, respectively, for the (Ba_(0.6)Sn_(0.4))(Zr_(0.5)Ti_(0.5))O₃composition. The highest rates were found for compositions that exceededthe percolation threshold for the A-site Sn(II) cations and the B-siteTi(IV) cations. These results demonstrate a route to highly metastableperovskites in order to target their smaller optical band gaps andfavorable photocatalytic properties.

The synthesizability of metastable semiconductors were explored herein,yielding a rich system of small bandgap photocatalysts for wateroxidation. The highest photocatalytic activities are found withincreasing metastability and Sn(II) substitution, as highlighted in FIG.54 upon crossing from the blue to the red shaded regions.

Example 2—Production of Lead-Free Piezoelectric Ceramics andApplications in Electronic Devices

One of the most widely used ceramics in the electronics industry is leadzirconate titanate, known as ferroelectric PZT, which shows a strongpiezoelectric effect. This material contains over 60% highly toxic leadby weight and can cause significant safety issues during its processingand use, as lead is volatile and easily released into the environment.In the manufacturing and use of PZT, lead exposure can come from directcontact as well as from its release into the soil, drinking water, andair. This problem has been broadly recognized in a number of largeindustries that utilize this material as a piezoelectric component.Regulating federal agencies around the world have been placingincreasingly stringent restrictions on the use of lead in commercialproducts and in manufacturing processes. The toxicity of PZT alsohinders important in vivo uses, such as in piezoelectric-poweredpacemakers and biocompatible sensors (Lu et al. Scientific Reports,2015, 5, 16065), as lead can slowly dissolve into a subject'sbloodstream. Lead is also one of the most common toxic elements found atSuperfund sites. While the increasing use of PZT represents a dangerousand growing concern, it also continues to be mass produced and utilizedin a plethora of products because there are currently no suitablereplacements for it.

A solution to this problem is the replacement of the lead content of PZTwith an equivalent, but far less toxic element, via a low-temperaturechemical reaction. This reaction replaces toxic lead with tin, which hasa significantly less toxic profile. For example, the tin content ofinorganic compounds is poorly absorbed with usually very low buildup inthe body. It also shows little to no evidence for being carcinogenic ormutagenic. The tin-based version of PZT, otherwise known as SZT, hasbeen forecasted to show equivalent or superior piezoelectric propertiesand to be an ideal replacement. Thus, a chemical process to prepare SZThas been highly sought after in industry and academia, but with no priorsuccess.

Described herein is a low-temperature process that exchanges lead fortin within PZT, resulting in lead-free SZT while retaining the samechemical structure as PZT. This chemical reaction occurs in inexpensiveand nontoxic solvents and occurs with an ion exchange that switches outthe lead for tin at near room temperature. These processing conditionsare favorable as compared to the significantly higher processingtemperatures of >1,000° C. needed to make PZT. The method describedherein is currently the only known method that can prepare SZT material.Furthermore, the method described herein can be used to replace leadfrom existing raw feedstocks of PZT.

A wide range of PZT-based industries is impacted by lead toxicity andrequires lead-free electronic substitutes. The lead-containing PZTpiezoelectrics are the basis for a multitude of applications thatinclude power sources, sensors, actuators, motors, and photovoltaics.For example, lead-containing piezoelectrics are used in ultrasound,electric lighters, microphones, fuses, guitar pickups, inkjet printers,loudspeakers, laser electronics among a multitude of many current deviceapplications and markets. The market size for piezoelectrics ispredicted to grow from ˜$23.54 billion (in 2016) per year to ˜$31.33billion per year, by the year 2022. In particular, there is a risingdemand for lead-free piezoelectrics in the automobile industry for usesin motors and actuators, and which currently represents the secondlargest market for PZT ceramics. Across all industries worldwide, themanufacture of lead-containing piezoelectrics is on the order of 1,250to 4,000 tons per year. This represents a growing field of companiesthat would benefit from supplying lead-free and environmentally benignreplacements, as well as in utilizing new manufacturing processes thatcan remove lead from their current PZT raw materials.

Example 3

Lead-containing ferroelectrics, such as PZT, are well known and widelycommercialized for their outstanding piezoelectric properties. Owing tothe toxicity of lead, lead-free substitutes have been highly soughtafter in industry. Disclosed herein, a range of low-temperature reactionconditions have been discovered in order to produce lead-freeferroelectric materials that can be further developed, for example, asenvironmentally-benign multilayer ceramic capacitors and aspiezoelectric transducers. The process involves replacing the toxicPb(II) cation with the isoelectronic Sn(II) cation that can function ina very similar chemical role. The methods can produce of lead-freeferroelectric films and single crystals.

The methods and products thereof described herein are moreenvironmentally friendly. The process described herein is performed at arelatively low temperature (e.g., from 50° C. to 250° C.), and usesinexpensive and nontoxic solvents. The methods described herein can beused to extract lead from existing materials used commercially.

The materials made using the methods described herein can be used aspiezoelectrics. Piezoelectrics have many widespread commercial uses asactuators, sensors and transducers, high voltage and power sources, andin photovoltaics.

Other advantages which are obvious and which are inherent to theinvention will be evident to one skilled in the art. It will beunderstood that certain features and sub-combinations are of utility andmay be employed without reference to other features andsub-combinations. This is contemplated by and is within the scope of theclaims. Since many possible embodiments may be made of the inventionwithout departing from the scope thereof, it is to be understood thatall matter herein set forth or shown in the accompanying drawings is tobe interpreted as illustrative and not in a limiting sense.

The methods of the appended claims are not limited in scope by thespecific methods described herein, which are intended as illustrationsof a few aspects of the claims and any methods that are functionallyequivalent are intended to fall within the scope of the claims. Variousmodifications of the methods in addition to those shown and describedherein are intended to fall within the scope of the appended claims.Further, while only certain representative method steps disclosed hereinare specifically described, other combinations of the method steps alsoare intended to fall within the scope of the appended claims, even ifnot specifically recited. Thus, a combination of steps, elements,components, or constituents may be explicitly mentioned herein or less,however, other combinations of steps, elements, components, andconstituents are included, even though not explicitly stated.

What is claimed is:
 1. A perovskite material comprising:[A_(1-x)Sn_(x)][Zr_(1-y)Ti_(y)]O₃ where: A is Ba or Pb; when A is Ba,then: x is from 0.1 to less than 1; and y is 0, 0.25, 0.5, or 0.75; whenA is Pb, then; x is from greater than 0 to less than 1; and y is from 0to less than
 1. 2. The perovskite material of claim 1, wherein theperovskite material comprises [Ba_(1-x)Sn_(x)][Zr_(1-y)Ti_(y)]O₃.
 3. Theperovskite material of claim 1, wherein the perovskite materialcomprises Ba_(0.8)Sn_(0.2)Zr_(0.25)Ti_(0.75)O₃,Ba_(0.8)Sn_(0.2)Zr_(0.5)Ti_(0.5)O₃, Ba_(0.6)Sn_(0.4)Zr_(0.5)Ti_(0.5)O₃,Ba_(0.4)Sn_(0.6)Zr_(0.5)Ti_(0.5)O₃,Ba_(0.8)Sn_(0.2)Zr_(0.75)Ti_(0.25)O₃, Ba_(0.8)Sn_(0.2)ZrO₃,Ba_(0.6)Sn_(0.4)ZrO₃, or a combination thereof.
 4. The perovskitematerial of claim 1, wherein the perovskite material comprises[Pb_(1-x)Sn_(x)][Zr_(1-y)Ti_(y)]O₃.
 5. The perovskite material of claim1, wherein the perovskite material is metastable.
 6. The perovskitematerial of claim 1, wherein the perovskite material is ferroelectric.7. The perovskite material of claim 1, wherein the perovskite materialcomprises a semiconductor with a bandgap that overlaps with at least aportion of the solar spectrum.
 8. The perovskite material of claim 1,wherein the perovskite material is biocompatible.
 9. A method of makinga perovskite material, the method comprising a peritectic flux reactionbetween a preliminary perovskite material and a Sn(II)-halide salt,thereby making a perovskite material comprising:[A_(1-x)Sn_(x)][B_(1-y)B′_(y)]O₃ where: A, if present, is selected fromthe group consisting of Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ba, Sc, Y,La, Ag, Cd, Tl, Pb, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb,Lu, or a combination thereof; B and B′, if present, are independentlyselected from the group consisting of Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni,Cu, Zn, Ga, Ge, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, La,Hf, Ta, W, Re, Os, Ir, Pt, Au, Bi, or a combination thereof; x is fromgreater than 0 to 1; and y is from 0 to 1; with the proviso that A and Bare different, A and B′ are different, and B and B′ are different. 10.The method of claim 9, wherein the method comprises contacting apreliminary perovskite comprising A[B_(1-y)B′_(y)]O₃ with aSn(II)-halide salt comprising SnCl₂ and/or SnF₂.
 11. The method of claim9, wherein the preliminary perovskite comprises lead zirconate titanate(PZT).
 12. The method of claim 9, wherein the perovskite materialsubstantially excludes lead.
 13. A method of converting alead-containing perovskite to a lead-free perovskite by extracting thelead from the lead-containing perovskite by performing a peritectic fluxreaction between the lead-containing perovskite and a Sn(II)-halidesalt, wherein the lead-free perovskite material comprises:[A_(1-x)Sn_(x)][B_(1-y)B′_(y)]O₃ where: A, if present, is selected fromthe group consisting of Li, Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ba, Sc, Y,La, Ag, Cd, Tl, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu,or a combination thereof; B and B′, if present, are independentlyselected from the group consisting of Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni,Cu, Zn, Ga, Ge, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, In, Sn, Sb, Te, La,Hf, Ta, W, Re, Os, Ir, Pt, Au, Bi, or a combination thereof; x is fromgreater than 0 to 1; and y is from 0 to 1; with the proviso that A and Bare different, A and B′ are different, and B and B′ are different.
 14. Amethod of use of the perovskite material of claim 1 as a photocatalystfor photocatalytic fuel generation, the perovskite material having abandgap, wherein the method comprises contacting the photocatalyst witha fuel precursor to form a mixture and illuminating the mixture withlight that overlaps with a least a portion of the bandgap of theperovskite material, thereby converting the fuel precursor to fuel. 15.The method of claim 14, wherein the fuel precursor comprises water orthe fuel comprises hydrogen.
 16. The method of claim 14, wherein theperovskite material exhibits a photocatalytic rate of from 100 μmol O₂h⁻¹ g⁻¹ to 5000 μmol O₂ h⁻¹ g⁻¹ under electromagnetic irradiation at oneor more wavelengths from 230 nm to 1023 nm.
 17. A device comprising theperovskite material of claim
 1. 18. The device of claim 17, wherein thedevice comprises a biocompatible sensor.
 19. The device of claim 17,wherein the device comprises a piezoelectric device.